CD4/CD8 ratio is considered as an emerging biomarker for human immunodeficiency virus (HIV)-related diseases. However, the relationship of CD4/CD8 ratio recovery and chronic kidney disease (CKD), and whether cumulative antiretroviral therapy (ART) is effective in the CD4/CD8 ratio recovery and in reducing CKD incidence among HIV patients remain unclear.A 17-year observational cohort study was conducted on all HIV-infected patients receiving ART in Guangxi, China. Kaplan–Meier analysis was used to investigate the cumulative CKD incidence. Cox regression and propensity score matching (PSM) were used to evaluate the association between CD4/CD8 ratio recovery and CKD incidence, and the effect of ART regimens on CD4/CD8 ratio recovery and CKD incidence.p < 0.001). Patients whose CD4/CD8 ratio did not recover to 0.7 had a higher CKD incidence than the patients who recovered , similar to the PSM analysis . Compared with the PI-based and INSTI-based regimens, NNRTI-based regimen had a better CD4/CD8 ratio recovery rate  and a lower CKD incidence .A total of 59,268 eligible individuals contributing 285,143 person-years of follow-up, with an overall CKD incidence of 9.65%. After ART, patients who developed CKD showed higher mortality than those with normal kidney function (12.48 vs. 7.57%, This large-scale real-world setting provide new evidence that the CD4/CD8 ratio recovery is associated with lower CKD incidence in HIV-infected patients receiving ART. NNRTI-based is a better choice for CD4/CD8 ratio recovery and reducing the risk of CKD. Antiretroviral therapy (ART) has significantly decreased the mortality of human immunodeficiency virus (HIV)/acquired immune deficiency syndrome (AIDS) patients. As patients live longer, chronic non-communicable diseases (NCDs) have become a prominent public health problem. Previous studies have shown that diabetes, hypertension, and chronic kidney disease (CKD) are important NCDs among HIV patients . In ChinLow CD4 cell counts and high viral loads have been considered as influencing factors for CKD in HIV-infected patients . CD4 celCumulative ART significantly decreases the estimated glomerular filtration rate (eGFR) of HIV patients and increases the risk of developing CKD . Additio2), available CD4/CD8 ratio measurements, treatment with ART, and triple treatment regimens  were included. Patients were excluded if they met the following criteria: (i) had no baseline CD4 cell count and/or CD8 cell count, (ii) did not have information to calculate baseline and follow-up eGFR, (iii) had a baseline eGFR <90 mL/min per 1.73 m2, (iv) were followed up for less than 6 months, (v) had a baseline CD4/CD8 ratio ≥1.0, or (vi) were treated with regimens other than NNRTI-based, PI-based and INSTI-based regimens. This study was approved by the Human Research Ethics Committee of Guangxi Medical University .We retrospectively collected data from December 2003 through October 2020 for all HIV-infected adults reported to the NFATP at the initiation of ART in Guangxi, China. Patients who had a normal baseline eGFR −(1.154 × age)−0.203]  and [(186 × serum creatinine)−(1.154 × age) − (Simplified MRDR formula). CKD was defined as eGFR lower than 60 mL/min per 1.73 m2  and defiP-value of 0.05 or less was considered statistically significant.Categorical variables were described as frequency while quantitative variables were expressed as the median ± interquartile range (IQR). A Kaplan–Meier graph was used to show the accumulative CKD incidence during the ART period, and statistical testing of differences was performed using the log-rank test. Multivariable Cox regression analysis was used to evaluate the association of CD4/CD8 ratio recovery and CKD incidence or ART regimen and CD4/CD8 ratio recovery or ART regimen combined with CD4/CD8 ratio recovery and CKD incidence. In addition, 1:1 propensity score matching (PSM) was used to match the characteristic variables between the CD4/CD8 ratio recovered and unrecovered groups, and 1:1:1 PSM was used to match the characteristic variables among the NNRTI-based, PI-based and INSTI-based groups. The forest plot was used to indicate the effect of the whole research population and the PSM population. Data were analyzed using the Statistical Package for the Social Sciences (SPSS) version 23.0 , R studio  and GraphPad Prism version 8.2 . A two-tailed statistical test with a 2). 53.30% patients had a CD4 cell count <200 cells/μL, 47.02% had a CD8 cell count ≤760 cells/μL. And 68.96% patients had a baseline CD4/CD8 ratio <0.30.A total of 110,890 HIV patients who initiated ART between December 2003 and October 2020 in Guangxi, China, were screened for inclusion in the present study. Of those patients, 51,622 were excluded, detail in P < 0.001) , and the overall mortality rate was 8.05% . The mortality in CKD patients was significantly higher than that in normal kidney function patients  .In our study, CD4/CD8 ratio recovery in only 11.72%  of patients when the restoration cutoff point was defined as 1.0 . In addition, 28.98%  of patients with a CD4/CD8 ratio recovery when the cutoff point was defined as 0.7 . UnivariP < 0.001, P < 0.001)  . Cox regression analysis showed that unrecovered CD4/CD8 ratio patients had a higher risk for CKD than recovery patients  or PI-based  regimens had a lower risk for unrecovered CD4/CD8 ratios than patients treated with INSTI-based regimens in all participants , we used 1:1:1 PSM analysis to match variables among these three groups to minimize potential biases. First, a caliper of 0.00001 was set to ensure that all demographic variables were properly matched between the NNRTI-based and PI-based groups, 13,159 NNRTI-based and 13,159 PI-based patients were included. Then, 13,159 NNRTI-based patients were properly matched to INSTI-based patients, 372 NNRTI-based and 372 INSTI-based patients were included at a caliper of 0.00001; similarly, 380 PI-based and 380 INSTI-based patients were also included at a caliper of 0.0000005. Finally, the three ART regimen groups of matched subjects were integrated, and a final number of 1,098 patients  were included. Chi-squared test was subsequently performed to evaluate the effectiveness of the PSM. The results showed that these demographic variables no longer exhibited statistically significant differences between each pair of ART regimen groups after matching (data not shown).P < 0.001) or PI-based  regimen had a lower risk for unrecovered CD4/CD8 ratios after PSM  or PI-based  regimen had a lower incidence of CKD than that of INSTI-based regimen (P < 0.001) ART regimen had a lower incidence of CKD than that of INSTI-based regimen  in several previous studies . The maiCD4 cell count has been considered as an influencing factor for NCDs in HIV-infected patients. With ART, the CD4 cell count in most patients gradually normalizes, but the CD8 cell count might remain at a high level, which leads to the CD4/CD8 ratio remaining low and difficult to recover to normal levels. In our study, the CD4 cell count did not necessarily raise to 500 cells/μL or above in patients whose CD4/CD8 ratio recovered to 0.7 . PreviouPrevious studies have reported that INSTI-based ART was associated with a greater increase in the CD4/CD8 ratio . In the Antiretroviral drugs have been shown to be associated with NCDs such as diabetes and obesity among HIV patients . SeveralIt should be noted that our study has some limitations. First, this was a retrospective cohort study, and we could not control some confounding factors, such as the use of medications other than the ART regimens, which might be associated with renal toxicity. Second, due to the lack of viral suppression data from the participants, it was not possible to determine whether patients’ viral load was suppressed when the CD4/CD8 ratio recovered to 0.7. Despite these limitations, to the best of our knowledge, this is the first large cohort study in a real-world setting to investigate the relationship of CD4/CD8 ratio recovery and CKD incidence in HIV-infected patients receiving ART. The recovery of the CD4/CD8 ratio is better, and the incidence of CKD is lower in HIV patients treated with NNRTI-based regimens than in those treated with PI-based or INSTI-based regimens. These results highlight the importance of monitoring the CD4/CD8 ratio in patients receiving ART, especially with PI-based or INSTI-based regimens.The original contributions presented in the study are included in the article/The studies involving human participants were reviewed and approved by the Human Research Ethics Committee of Guangxi Medical University. Written informed consent for participation was not required for this study in accordance with the National Legislation and the Institutional Requirements.JJ, LY, SQ, and HaL conceived and designed the study. FQ, JJ, QL, and WH conducted the data analysis and literature review and drafted the manuscript. FQ, QL, WH, DW, KH, and KL involved in the study supervision, data collection, and interpretation of the data. FQ, RC, JL, BL, and HuL assisted with data management and data analysis. All authors contributed to the revision of the manuscript and approved the final version.The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors and the reviewers. Any product that may be evaluated in this article, or claim that may be made by its manufacturer, is not guaranteed or endorsed by the publisher.


A major challenge in the management of antiretroviral therapy (ART) is to improve the patient’s adherence, reducing the burden caused by the high number of drugs that compose the treatment regimens for human immunodeficiency virus positive (HIV+) patients. Selection of the most appropriate treatment regimen is responsible for therapeutic success and aims to reduce viremia, increase the immune system response capacity, and reduce the incidence rate and intensity of adverse reactions. In general, protease inhibitor (PI) is one of the pillars of regimens, and darunavir (DRV), in particular, is frequently recommended, along with low doses of enzyme inhibitors as cobicistat (COBI) or ritonavir (RTV), by the international guidelines. The potential of clinically significant drug interactions in patients taking COBI or RTV is high due to the potent inhibitory effect on cytochrome CYP 450, which attracts significant changes in the pharmacokinetics of PIs. Regardless of the patient or type of virus, the combined regimens of DRV/COBI or DRV/RTV are available to clinicians, proving their effectiveness, with a major impact on HIV mortality/morbidity. This study presents current information on the pharmacokinetics, pharmacology, drug interactions, and adverse reactions of DRV; it not only compares the bioavailability, pharmacokinetic parameters, immunological and virological responses, but also the efficacy, advantages, and therapeutic disadvantages of DRV/COBI or DRV/RTV combinations. The human immunodeficiency virus (HIV), responsible for the development of acquired human immunodeficiency syndrome (AIDS), is today one of the most serious public health challenges that humanity has to deal with . Nearly Another major benefit of ART is the possibility of preventing virus transmission, as this therapy manages to significantly reduce the number of maternal–fetal transmissions . Highly Patients with HIV infection may face increased risk of cardiovascular disease, neurocognitive disorders, liver disease, cancer, and bone demineralization. These comorbidities are not only attributed to the disease per se, but are considered, in some cases, side effects of ART. Comorbidities can also be caused by continued viral replication in so-called “sanctuaries,” or they can be consequences of chronic HIV inflammation. Nowadays, only a third of deaths among people infected with HIV are caused by the natural course of the disease. The rest of the deaths occur due to comorbidities, complications induced by drug interactions and toxicity of ART .ART can inhibit viral replication, controlling the infection and thus prolonging the patient’s life. Moreover, people infected with HIV can lead a normal life for decades. However, even patients who initially responded well to the treatment may experience moments or periods of therapeutic failure. This failure can be caused by many factors: low/lower patient adherence, too low potency of the drug, viral resistance, cellular characteristics, and pharmacokinetic considerations .There is an apparently large number of medicinal substances (30 molecules) available to HIV infected patients. Treatment regimens always include combinations of ARV drugs . The treIt is known that HIV has the great ability to make genetic mutations. There are significant zonal differences in the type of virus, which requires in-depth study related to its evolution in the body, depending on the geographical region and genetics of the infected population.This study aims to provide the main information on the topic related to ART usage in HIV-infected patients, especially regarding those in whose regimen a protease inhibitor (PI)—namely darunavir (DRV)—is introduced in combination with an enzyme inhibitor (a booster), which increases the ARV effect of PI. The pharmacokinetic of the PIs is significantly influenced when combined with ritonavir (RTV) or cobicistat (COBI) (both are boosters); therefore, a detailed analysis of changes in pharmacokinetic parameters is required in patients with this regimen. Management of ART involves choosing the best treatment regimen for the therapeutic success . The article reviews information from the literature relevant to the topic. At this time, there is not much comparative data between the advantages and disadvantages of using one inhibitor or another, or to strictly compare the values of boosted pharmacokinetic parameters.fixed dual combinations—emtricitabine/tenofovir, COBI/DRV, lamivudine/zidovudine, lopinavir/RTV, and abacavir/lamivudine;fixed triple combinations—abacavir/lamivudine/zidovudine and abacavir/lamivudine/dolutegravir;fixed quadruple combinations—elvitegravir/COBI/emtricitabine/tenofovir.The main classes of ARV drugs comprise 30 molecules active against HIV-1 as follows: nucleoside or nucleotide reverse transcriptase inhibitors (NRTIs), non-nucleoside reverse transcriptase inhibitors (NNRTIs), integrase inhibitors, PIs, and pharmacokinetic enhancers (boosters). In addition, there are new fixed dose combinations between various molecules, designed to improve administration and thus achieve adherence:In the life cycle of HIV, the protease is an essential element for viral maturation. HIV protease is a homo dimeric aspartyl protease, each monomer being composed of 99 amino acid residues with a catalytic aspartic acid (Asp) at position 25. HIV-1 protease cleaves the precursor of Gag (Gag) and Gag-Pol polyproteins encoded by the HIV genome-1 at nine processing sites to produce mature active proteins. Pol-polyproteins are first cleaved from Gag-Pol polyproteins and then further digested into protease, reverse transcriptase (p51), H ribonuclease (RNase H) (p15), and integrase .The active site is not fully exposed, being covered by two flaps, which must be opened to allow the substrates to access it. HIV-1 protease activity can be inhibited by blocking its active site. The indispensable role of HIV protease in viral maturation makes it a major target of ARV drugs. A large number of HIV protease protein structures have facilitated the formulation of new and improved inhibitors .The first PI approved by the United States was RTV (1996), shortly followed by indinavir (1996), nelfinavir (1997), saquinavir (1997), amprenavir (1999), lopinavir/RTV (2000), atazanavir (2003), fosamprenavir (2003), tipranavir (2005), and DRV (2006). The potency of these agents is similar, the choice of one of them in therapy is made taking into account the pharmacokinetics (regardless of how many times they are administered/day), tolerance, and the presence of antiviral resistance. Most HIV PIs are metabolized by the liver through enzymes that metabolize the drug cytochrome P450 (CYP450). Importantly, all approved HIV PIs have a high potential for drug–drug interactions due to their ability to inhibit drug metabolizing enzymes, most commonly cytochrome P450 3A4 (CYP 3A4) ,11.RTV is the strongest inhibitor of CYP 3A4 and, for this reason, is often combined in small doses (100 to 200 mg daily) with other PIs to produce a booster effect, increasing plasma levels and the half-life of the protease, without significantly increasing side effects ,13.COBI is a newly introduced pharmacological enhancer that has inhibitory activity against several drug metabolizing enzymes in addition to CYP 3A4 including CYP 2D6 and the P-glycoprotein (P-gp) transporter, making it an important agent. It is used in therapy when the increase in active substance levels of agents metabolized by the cytochrome P450 system is desired, being available as 150 mg tablets .Ten HIV PIs are currently available: saquinavir, indinavir, RTV, nelfinavir, amprenavir, fosamprenavir, lopinavir, atazanavir, tipranavir, and DRV. PIs represent the largest class of drugs used in the fight against HIV. These substances block the activity of HIV protease, an enzyme that the virus uses to break down high-mass polyproteins into smaller units needed to assemble new viral particles .PI acts in the late stage of the HIV replication process. When the virus infects a cell, its replication systems are forced to produce long viral precursor proteins. These precursors are grouped so that they are able to leave the cell, causing cell lysis and its death. Even before proteins leave the cell, they must be cleaved by an enzyme called “HIV protease” . The protease acts in the budding virion, causing the morphologically distinguishable immature virions to mature. At such a late stage in replication, the benefit of this action is the relatively small locus of activity. The requirement that all viral proteins be enzymatically cleaved at this location creates a blockage and involves a very specific and effective action of disrupting viral replication. However, there is a disadvantage of this mechanism, namely that these substances are not potentiated and acted upon at the initial time of infection. Thus, PIs have a virustatic rather than a virucidal effect .However, HIV can still replicate (even in the presence of PIs), but the resulting virions are immature and do not have the ability to infect new cells. All molecules currently known to act by inhibiting HIV protease are metabolized by CYP450, especially by the CYP3A4 isoenzyme group.0, then at 1, 2, 3, and 4 h) may be helpful to clinicians in understanding whether the maximum concentration and prolonged exposure exceed the therapeutic safety limits.If a CYP 3A4 inhibitor (RTV or COBI) is administered associated with both fluconazole  and atazanavir (PI), the rate of metabolization of all ARVs decreases, leading to their increased concentration in plasma. The action of other drugs also metabolized by CYP 3A4 isoenzymes  will be potentiated, increasing the risk of toxicity or, conversely, blocking the activity of other substances by hepatic metabolism. CYP3A4 inducers decrease the PI concentrations although this effect has been shown to counterbalance the effect of stimulators. When concentration problems occur, monitoring plasma concentrations  have some structural similarities and a similar binding pattern, which may be responsible for some of the common side effects of the regimens containing them.ART promotes the development of resistant viral variants extremely fast, within a few days or weeks from the moment of incomplete suppression of replication . The virHIV-1 protease is prone to resistance development largely due to the process in which it is synthesized in vivo. Reverse transcriptase creates viral deoxyribonucleic acid (DNA) from viral ribonucleic acid (RNA) that is embedded in the virus host cell during infection. This process, unlike eukaryotic DNA synthesis, is highly prone to errors due to the lack of correction mechanisms, causing HIV-1 to develop many polymorphic mutations ,31.The high error rate of this process increases the probability that genetic mutants will be introduced into the system being influenced by the evolutionary pressures of PIs. Consequently, the resistance development is exacerbated and persistent due to the limited ability of many PIs to maintain effective concentrations in the body and/or to reach the desired sites of action such as the central nervous system (CNS) . The CNSTo improve the effective penetration of PIs, strategies have been used to increase the ability to cross the blood–brain barrier (BBB) by increasing the lipophilic nature of inhibitors and introducing fluoride into the structure in different positions ,34.Resistance to PIs occurs due to mutations in the HIV protease. Currently, about 10–20 such mutations are known. Frequently, multiple mutations can occur/exist in the same patient, which leads to the appearance of totally different enzymatic structures . PublishUnique amino acid substitutions in the cavity of the active site of the enzyme, altering the size and shape of the side chains, which may alter the affinity of the drug and preserve the catalytic activity. The known mutations of this type are D30N, V32I, I47V, G48V, I50V, Val82, I84V, and G48T/L89M .Mutations that reduce the stability of the protease dimer, increasing dissociation between these portions and releasing limited inhibitor. The mutations associated with this mechanism are L24I, I50V, F53L, and Ile50 .Distal mutations, also related to PI resistance, may occur in different ways and may be difficult to detect, but may promote structural changes until the interaction with the inhibitor changes ,45. DistThe evaluation of the structural changes and the activity of the mutant proteins highlighted three categories of mutations, as follows:The highest resistance to PIs is correlated with primary and secondary mutations in the protease gene. Primary mutations are caused by changes in the active locus of the protease; secondary mutations help restore viral protease activity, increasing viral replication capacity. Typical examples are V82A/F/T mutations, which contribute to the resistance to many PIs including lopinavir/RTV, atazanavir, fosamprenavir, nelfinavir, and saquinavir. Cross-resistance to other ARVs has also been studied in people infected with HIV using more than 6000 clinical isolates. These studies indicated that 59–80% of isolates had reduced susceptibility to indinavir (IDV), RTV, nelfinavir (NFV), and saquinavir (SQV), among other PIs .The most common and general approved PIs have lower than optimal pharmacokinetic properties. This is due to the fact that PIs are only substrates for the CYP3A4 isoenzyme  .As a result, numerous approved PIs have low plasma levels and short half-life. Interestingly, some PIs act as both inhibitors and inducers of isoenzymes. As it turns out, RTV is a potent inhibitor of CYP3A4 and the administration of a low dose of RTV with PI significantly improves the pharmacokinetic parameters of PIs. PIs such as DRV, fosamprenavir, and atazanavir can be given as a once daily dose when given with a low dose of RTV .However, the use of RTV as a pharmacokinetic booster may raise some issues. When RTV is used as an enzyme inhibitor for other classes of antiviral compounds in HAART that does not contain PI, a subtherapeutic dose of RTV may accelerate the onset of PI-resistant HIV-1 variants . Multi-rUnlike RTV, COBI will not contribute to the development of drug-resistant HIV-1 variants. The formulation of a PI with COBI resulted in an all-in-one pill, convenient for patients, resulting in increased adherence by reducing the pill burden. While this regimen has improved the pharmacokinetic properties of currently approved PIs, a PI design that does not require a pharmacokinetic booster is the ideal option.Pharmacokinetics describes the quantitative aspects of the pathway of the drug substance in the body after administration . Figure Absorption may take some time; the interval elapsed from the time of administration until the occurrence of a certain level of concentration in the blood is called “lag time”—the period of delay. Absorption determines the level of plasma concentration . The staIf the distribution takes place faster than elimination, a biphasic decline will be observed on the curve. The first curve that will decrease, much faster, results from the distribution of the drug in the compartments of the body. The second curve occurs later, is slower, and represents a decrease in the plasma concentration of the substance after elimination . The time when/at which the plasma concentration of the drug falls below 50% is called the half-life (t1/2). Due to the different distribution and elimination, there are two half-lives, but in practice, no distinction is made between them ,55.At the end of the dosing interval, before the ingestion of a new dose, a residual concentration (Ctrough) is reached, which is most often equal to the minimum concentration (Cmin). The area under the curve (AUC) is a pharmacokinetic parameter that measures drug exposure over the entire dosing interval, without providing information if these pharmacokinetics have a dynamic profile  and the minimum concentration (Cmin)) .In the case of ARV drugs, this link between active substance concentrations, efficacy, and toxicity levels has been demonstrated, therefore Cmax, Cmin, and AUC are significant parameters. They indicate the degree of ARV exposure, either at a certain point in time (Cmax and Cmin) or at a certain time interval. The pharmacokinetics of any drug change with a single dose or with repeated doses. When the pharmacokinetic profile does not change after the next dose, an equilibrium level is reached, called the steady state. The time to reach this threshold is different and depends on a number of factors. Among ARV drugs, those that are capable of inducing CYP 450 enzyme systems need 14 days to reach steady state plasma levels .Another important factor in reaching the level of therapeutically effective plasma concentration is the binding to plasma proteins. The most important plasma proteins are albumin and alpha I-acid glycoprotein (AAG). AAG mainly binds HIV PIs and has a wide variety depending on race, body mass index (BMI) (stronger in those with high body mass index), and the stage of HIV infection (strong binding in the acute phase of the disease). Most ARV drugs are bound to plasma proteins, sometimes even completely. Only the free, unbound fraction is pharmacologically active, so the factors that prevent this binding influence the effectiveness of the therapeutic agent. The determination of the plasma drug concentration takes into account both the bound and the unbound fraction of plasma proteins .It is known that pharmacodynamics studies explain and describe the response/concentration relationship. When this correlation exists, plasma levels can be manipulated by adjusting the dose in order to obtain concentration values within a desired necessary therapeutic window . In practice, therapy monitoring can be used to correctly adjust the dose. If low doses are given for long periods of time and the level of plasma concentration falls below the optimum concentration, there is an increased risk of therapeutic failure due to the appearance of viral resistance and ART will be ineffective. On the other hand, too high doses of drug are associated with an increased risk of toxic effects, influencing the patient’s quality of life, with immediate consequences on their adherence to treatment .The pharmacokinetics of ARV substances are extremely different, depending on the concentration but also on the patient, with multiple side effects and high toxicity. Clinical studies have shown that there is a great variety in terms of therapeutic response, from one patient to another or for the same patient, depending on many variables/circumstances ,54,55,56Oral bioavailability of PIs is generally considered to be weak or variable . On average, the time to Cmax among agents is 3 h , with a median half-life of approximately 6 h. The elimination half-life varies between 3 and 15 h. Except for indinavir , all PI agents are extensively bound to proteins (>90%). Of all the pharmacokinetic parameters, the metabolic considerations on PIs may be the most worrying. This is especially true for patients receiving poly-medicine . PIs are inducers and substrates of multiple cytochrome P450 (CYP) isoenzymes including CYP 3A4, CYP 2D6, CYP 2C9, and β-glycoprotein.Compared to other classes of ARVs, PIs have unique characteristics that justify their prescription compared to other classes of drugs .A recent study pointed out that the intrinsic antiviral potency  may be higher for PIs than for other classes of ARV drugs. This observation is based on the fact that nucleoside analogues and integrase inhibitors target reactions in which a single enzyme complex and viral nucleic acid mediate a key step. Instead, PIs target the entire number of enzymes .Studies have found that PIs show residual ARV activity, even in individuals who have already developed resistance to other antiretrovirals. A significant proportion of newly developed viruses will remain partially sensitive to PIs for some time. This explains the need to continue a failed treatment regimen with PIs instead of eliminating them, in the case of patients who have no other treatment options. This is because the use of PIs is associated with low viral load and viremia below 10,000 copies/mL, which does not lead to a decrease in CD4, at least for 1–2 years ,59.Several studies comparing NNRTIs and PIs have shown that cluster gains of differentiation 4 (CD4) are generally higher using PIs than NNRTIs, even without dose adjustment in the case of patients undergoing complete viral suppression ,61,62.Reduced immune activation ;Reduction of CD4+ cell apoptosis ,65;Decreased fitness of PIs-resistant viral variants ;Affected replication of PIs-resistant viruses in T-cells (tymocytes) .From a clinical point of view, these characteristics make PIs a preferred class of ARVs, especially in patients with very low CD4 counts and whose priority is rapid immune restoration.One of the main limitations of most PIs is the low penetration into the central nervous system (CNS). This feature may not be relevant in the case of ARV regimens in triple combinations .The availability of PIs marked an important step in the treatment of HIV infection. However, there was a significant cost in terms of quality of life because first-generation PIs required complex dosing and had significant side effects. The latest PIs have overcome these limitations with a more convenient dosage  and a favorable safety profile and greater potency. The pharmacokinetic profile has improved considerably with low doses of RTV, and PIs continue to be key agents in the treatment of HIV . The maiTo minimize the metabolism of these enzymes, pharmacokinetic enhancers (PK enhancers) like RTV and COBI are used as ART due to their ability to inhibit CYP3A4, CYP3A5, and CYP2C9; this reduces the dose and frequency of PI administration ,72. MoniPeople living with HIV must follow strict treatment regimens to prolong their lives and reduce mortality . Lack ofThe most common side effects reported by patients treated with PIs are as follows: sexual dysfunction, gastrointestinal disorders , liver disorders, pancreatitis, cardiovascular disease, rash, and metabolic disorders. ARV intolerance and toxicity are the cause of frequent changes in treatment regimens. Unfortunately, this change also leads to the emergence of resistance ,87,88,89Progress in treatment and individualization of doses has led to fewer side effects compared to the initial regimens. Today, less than 10% of naive patients (those who are in the first treatment regimen) on ART still experience adverse events that could limit the treatment. Even so, long-term complications persist, especially the appearance of insulin resistance and disorders related to lipid metabolism. Therefore, it is necessary to continue monitoring the complete blood count and metabolic profile of these patients. Tests should be performed every three to six months, being also necessary an annual analysis of the urine (in order to verify proteinuria) and a lipid profile; if the treatment schemes are changed, the tests must be done again, respecting the periodicity ,89,90.Insulin resistance is a common subject in HIV patients, contributing to dyslipidemia and impaired glucose metabolism . Immune Metabolic disorders associated with PI therapy are the most problematic adverse events that may occur, their incidence varying from drug to drug. These disorders include hyperlipidemia, abnormal fat distribution (lipodystrophy), and impaired glucose tolerance, which are thought to be due to peripheral insulin resistance. Clinicians caring for patients treated with PIs should be alert to adverse events, especially those involving changes in lipid and glucose metabolism . Lipid dTwo studies published in 2007 on 25,000 patients showed that the use of PIs is directly correlated with myocardial infarction ,97. The Lipodystrophy is the redistribution of fat, with accumulation on the throat and abdomen, occasionally forming a “buffalo hump” , being usually associated with fat loss from the face, buttocks, and extremities. This disorder is resistant to treatment, often not reducing even with the discontinuation of the triggering agent. Some patients become unrecognizable after the treatment because of the body and facial feature alterations, many of them resorting to plastic surgery for some relief. Glucose intolerance, which sometimes leads to diabetes and genuine diabetic ketoacidosis, have been reported more and more frequently .Hyperlipidemia is closely associated with both hyperglycemia and redistribution of fat and may put HIV patients receiving HAART at increased risk for cardiovascular disease . PIs supMany patients experience gastrointestinal symptoms at the beginning of treatment with PIs or when switching from one regimen to another. These symptoms frequently lead to discontinuation of therapy and can be a major obstacle to efficient treatment . The stuSexual dysfunctions occur more frequently in patients treated with PIs than in patients treated with other substances . There aMild to moderate increases in serum aminotransferase and alkaline phosphatase levels that occur in a large proportion of patients taking ARV regimens containing PI. Moderate to severe increases in serum aminotransferase levels  are found in 2% to 18% of patients, depending on the agent, the frequency of monitoring, and most importantly, the presence of virus coinfection with hepatitis B (HBV) or C (HCV). In HIV patients, without HCV or HBV infection (“mono infection”), increases in alanyl aminotransferase (ALT) and aspartate aminotransferase (AST) are uncommon; levels of more than five times the upper normal limit were reported in only 1–4% of patients. These increases are usually asymptomatic and self-limiting and can be resolved even with continued medication. Therefore, this should not be a reason to discontinue the medication.Hyperbilirubinemia, without other manifestations of liver damage, is caused by the inhibition of glucuronyl transferase UDP, the liver enzyme responsible for conjugating bilirubin that is deficient in Gilbert’s syndrome. Hyperbilirubinemia is usually mild, averaging 0.9–1.5 mg/dL, but may be more severe in patients with Gilbert’s syndrome with increases of 2.5 mg/dL or more and clinical jaundice. Jaundice, however, does not indicate liver damage. However, jaundice caused by PIs can be painful for the patient and is a reason to discontinue treatment.Acute, idiosyncratic liver damage has been reported in most agents not very frequently. The few reported cases usually occurred within one to 12 weeks after starting therapy, and the pattern of serum enzyme growth ranged from hepatocellular to mixed and cholestatic. Signs of allergy or hypersensitivity  may also occur as well as the appearance of autoantibodies. Acute liver damage from PIs is usually self-limiting but severe and isolated cases of acute liver failure have been reported, especially in patients with pre-existing underlying liver disease.Exacerbation of chronic underlying hepatitis B or C in co-infected individuals. Hepatitis usually occurs in 2–12 months after starting therapy, being associated with a hepatocellular pattern of serum enzyme growth, and also by increases, followed by decreases in the serum levels of HBV DNA or HCV RNA. These fluctuations can be severe, and even fatal cases have been reported .All drugs in the class of PIs have been associated with liver damage. About a third of patients treated with PIs have liver problems associated with high levels of enzymes. Most of the time, these reactions are mild and transient . PIs areDrug interactions are the cause of many of HAART complications. Among them, an important role is played by the inhibition, respectively the enzymatic induction produced by PIs as well as the interactions of the P-glycoprotein.Enzymatic inhibition occurs when a substance blocks or reduces the activity of metabolic enzymes. The net effect is to increase plasma levels and the effects of the parent compound, while preventing the formation of metabolites and reducing elimination. All PIs are inhibitors of cytochrome 450, especially in the CYP 3A4 isomorph. From this point of view, PIs behave similarly to ciprofloxacin, erythromycin, clarithromycin, diltiazem, itraconazole, or ketoconazole. They all inhibit CYP 3A4 and affect the pharmacokinetics of low therapeutic index substances. For example, in patients treated with carbamazepine, vomiting and dizziness, increased liver enzyme levels, and increased serum anticonvulsant levels were observed 12 h after a dose of RTV . Even otThe metabolism of the PIs is, in turn, affected by other potent 3A4 inhibitors, because all PIs are metabolized by the enzyme 3A4. Any substance with a stronger inhibitory effect on 3A4 can slow down the metabolism of PIs. The other potent inhibitors that influence the rest of the PIs include ciprofloxacin, clarithromycin, diltiazem, erythromycin, itraconazole, nefazodone, and grapefruit juice. Inhibition of PI metabolism by these agents may increase their efficacy or reduce the dose required (as seen when RTV is used to potentiate other PI). However, there is also an adverse reaction such as worsening of side effects and toxicity, which leads to an increased risk of events such as headaches, nausea, diarrhea, hepatitis, and pancreatitis. All lead, in the end, to non-adherence. It should be mentioned that the interruption of the potent inhibitor, other than PIs, entails a return to the uninhibited state, but also a rapid reduction in circulating levels of PI, which puts the patient in danger of developing viral resistance to the entire class of PIs.This represents the phenomenon of increase or acceleration of metabolic enzyme activity, under the action of a substance or a compound. The net effect is to decrease the levels of the parent compound and its effects, while increasing the production of metabolites and the amount available for elimination. Rifampicin, carbamazepine, phenytoin, ethanol, and barbiturates are potent inducers of many enzymes belonging to the CYP 450 family . InductiThese glycoproteins are responsible for the outflow or “pumping” of substances outside the cells and are the “guardians” that influence the bioavailability and pharmacokinetics of drugs in the intestine and liver and prevent the penetration of the drug into the brain, testicles, and placenta. PIs are all substrates of P-glycoproteins, which may explain why it is difficult for ARVs to cross the blood–brain barrier or other sanctuaries. When P-glycoproteins are inhibited, the concentration of the drug increases, especially if it is a substrate for the P-glycoprotein. RTV initially inhibits the P-glycoprotein, which may allow other substrates to reach higher serum levels, either in the intestinal wall or in the blood–brain barrier. This inhibition of P-glycoprotein, together with 3A4 inhibition, would have an additive inhibitory effect and would increase the level of substrate drugs for P-glycoprotein and CYP 3A4. In vitro, long-term RTV exposure induces P-glycoprotein expression, reducing the drug ability to ‘cross the barrier’, and effectively reducing the bioavailability of P-glycoprotein as a substrate ,111.ART combined with two or more PIs has changed the standard of care in the treatment of HIV infection. Two PIs regimens such as DRV/RTV are commonly used as initial therapy with PIs. As viral resistance increases and the development of new PIs decreases, clinicians resort to dual RTV-boosted PIs to treat patients. The potency of these combination therapies is increased, while the burden of pills, dietary restrictions, and often side effects are reduced. These clinical advantages lie in the improvement of the pharmacological properties of the substances, in particular, through changes in pharmacokinetics (absorption and metabolism). Changes are occurring in the absorption and metabolism of PIs when co-administered with a cytochrome P450 enzyme inhibitor (CYP) . The ability of RTV to increase concomitant plasma concentrations (Cmin) of co-administered PI is probably the greatest clinical benefit of dual therapy, as inadequate ARV concentrations may support long-term ARV resistance.The fact that there is a close link between the therapeutic response and the plasma concentration of the drug substance is certain. Studies show that inadequate levels of circulating substance play an important role in therapeutic failure and the emergence of viral resistance . Low adhRTV also has tolerability problems in a large number of patients. Other disadvantages of RTV are that it inhibits/induces other enzymes that metabolize drugs, resulting in a significant number of drug-drug interactions . Based oCOBI’s CYP 3A4 inhibitory potency is similar to that of RTV . A totalCOBI is marketed as a single agent or in fixed combinations, in association with atazanavir, DRV, or elvitegarvir. The two boosters, COBI 150 mg/day and RTV 100 mg/day, may be interchangeable with similar therapeutic results. However, clinicians prefer the administration of 150 mg COBI as a boosting agent for CYP 3A4 metabolites rather than RTV due to its higher specificity and the fact that it has no enzyme induction effect. Hence, the profile of interaction with other drugs is different.RTV, marketed as Norvir; it is included in Kaletra—lopinavir/RTV;COBI, commercially called Ybost; it comes in many combinations: atazanavir/COBI (Evotaz), elvitegravir/COBI/emtricitabine/tenofovir (Genvoya), DRV/COBI (Resolve), elvitegravir/covetousness/emtricitabine/tenofovir disoproxil (Stribild), DRV/COBI/emtricitabine (Symtuza).Although both COBI and RTV have similar boosting profiles for CYP3A4 and can be used with the same therapeutic efficacy, COBI is preferred due to its greater specificity and the absence of inducing properties. In addition, the two substances interact differently with other biochemical/medicinal substances metabolized by the following enzymes: CYP1A2, CYP2B6, CYP2C8, and CYP2C9. In this context, one of the biggest challenges for clinicians is to adjust doses in patients with multi-drug therapy:37H48N6O5S2, is an ARV drug in the class of systemic PIs used in combination with other drugs for the treatment of HIV/AIDS. It was approved for commercialization on 1 March 1996, becoming the seventh ARV and the second PI entering the U.S. market. This class of ARVs has played an extremely important role in reducing the number of deaths caused by HIV/AIDS. The introduction of HAART at that time in the United States led to a decrease in the annual death rate from 50,000 to 18,000 . T. T127]. From the analysis of the 2D diagram, it is revealed that RTV binds to the following amino acids of the wild type HIV-1 protease: GLY27, ALA28, VAL32, ASP29, ALA82, ALA28, PRO81, ARG8, and ILE47. ASP25 forms hydrogen (H) bonds to the oxygen in the HIV protein side chain, ALA28 and PRO81 form π–alkyl bonds via chains A and B. The amino acids ALA28 and ILE50, in the HIV-1 chain A and B establish π–alkyl and alkyl bonds with RTV. ILE47 and ALA28 form a π–alkyl bond with the 1,3-thiazole group of the ligand, ASP30 through C–H, and ALA82 through both the C–H and the π–alkyl bonds. ARG8 bonds via π–cationic with the protein.In RTV docking with the B-chain of HIV-1, the main link is π–alkyl. PRO81 is formed by the pyrolidine protein bond through the benzene ring. The amino acid ASN25 in the A chain as well as in the B chain  bonds and interacts at the same oxygen atom in the ligand structure.ILE84 forms a π–alkyl bond with benzene and C-alkyl in the ligand side chain. VAL32 binds by alkyl, and GLY27 and ASP25 by the H bond. ASP29 and GLY49 to O, in the side chain, form the C–H bond, and ASP29 also forms the H bond. Absorption. According to the summary of product characteristics (SPC), a study of HIV-infected volunteers evaluated the pharmacokinetics of RTV multiple-dose regimens during fasting. RTV accumulation was observed to be slightly lower than that calculated on a single dose basis due to an increase in apparent dose-dependent clearance. Over time, the plasma concentration of RTV before the next dose decreases, possibly due to enzyme induction, but appears to stabilize after two weeks of treatment. The time to peak plasma concentration (Tmax) remained constant—approximately 4 h as the dose increased. Renal clearance was on average less than 0.1 L/h and relatively constant over the entire dosing range. It has been observed that foods slightly decrease the bioavailability of RTV film-coated tablets, especially foods with moderate and high lipid content .Distribution. The apparent volume of distribution (VB/F) of RTV is approximately 20–40 L after a single 600 mg dose. In humans, RTV has been shown to be 98–99% bound to plasma proteins and is consistent at concentrations between 1.0–100 µg/mL. RTV binds with comparable affinities to both alpha-1 acid glycoprotein (GAA) and human plasma albumin (APU). Studies in rats have shown that the highest concentrations of RTV are achieved in the liver, adrenal glands, pancreas, kidneys, and thyroid. The tissue/plasma ratio was approximately 1 in the lymph nodes in rats, indicating that RTV is distributed in the lymph tissue. It slightly penetrates into the brain .Drug metabolism. RTV is extensively metabolized by hepatic cytochrome P450, mainly by CYP 3A4 isoenzymes and, to a lesser extent, by CYP 2D6 isoforms. Animal and in vitro studies with human liver microsomes have shown that RTV is oxidatively metabolized. In humans, four metabolites of RTV have been identified. The major metabolite is isopropyl-thiazole (M-2), with antiviral properties similar to the parent compound. However, the AUC of metabolite M-2 was approximately 3% of that of RTV .Clearance. RTV is eliminated primarily by the hepatobiliary route. Approximately 86% of the radiolabeled molecules were found in feces, some of which is thought to be unabsorbed RTV. In studies, the renal route has not been shown to be a major route of elimination of ritonavir .The RTV target organs are the liver, retina, thyroid gland, and kidneys. Hepatic changes involved hepatocellular, biliary, and phagocytic structures and were accompanied by increases in liver enzymes. Human clinical trials did not reveal RTV-induced ocular changes. All thyroid changes were reversible upon discontinuation of RTV. Clinical investigations did not show significant impairment of the thyroid function tests or significant renal impairment in humans. There were observed various side effects: common (at low doses): diarrhea and increased lipid levels; and rare: changes in heart rate, severe allergies (hypersensitivity reactions) and eczema (Steven-Johnson syndrome) ,72,129.40H53N7O5S2) is a structural analogue of RTV, in which the valine fragment was replaced with a 2-morpholinethyl group and the hydroxyl group was removed. These changes cancel out the anti-HIV activity per se of COBI, retaining only the highly inhibitory and selective effects on the CYP 3A protein isoenzyme family [Cobicistat -2- methyl) (methyl) carbamoyl- amino)-4-(morpholin-4-yl) butanoic acid with the amino group of 1,3-thiazol-5-ylmethyl -5-amino-1,6-diphenylhexane-2-yl) carbamate, COBI has a molecular weight of 776 (g/mole), good solubility, and terminal half-life of 3–4 h. Plasma protein binding is 97–98% and CSF to plasma ratio is 1.1% .It acts as a pharmacokinetic enhancer in the treatment of HIV-1 by inhibiting the CYP P450 enzymes responsible for the metabolism of other drugs. It works as a CYP450 inhibitor. It belongs to the class of 1,3-thiazoles, but also to the class of morpholines, urea, is a carbamate ester and an amide of monocarboxylic acid. The chemical structure of the substance is shown in Selective inhibitor of cytochrome P450 (subfamily CYP3A enzymes) with RTV-like potency, and COBI inhibits the mechanism of action of these enzymes. Inhibition of CYP3A-mediated metabolism enhances systemic exposure to drugs that are substrates for CYP3A (atazanavir or DRV), which have limited bioavailability after oral administration and a reduced half-life due to CYP3A-mediated metabolism. The inhibitory effect of COBI is also manifested on other enzymes: CYP 3A4, CYP2D6, P-gp, OATP1, MATE1, and BCRP . COBI doProvided in the form of a film-coated tablet, COBI assures 150 mg active substance concentration. It is indicated as a pharmacokinetic enhancer for atazanavir 300 mg once daily, or DRV 800 mg once daily, as one of the components of ART combination in HIV-1 infected adults. It is recommended to be co-administered orally, both food and the drug. The tablet should not be chewed or crushed. COBI is formulated in fixed doses with atazanavir, DRV, and tenofovir/emtricitabine/elvitegravir .n = 68) were 1.2 ± 0.3 µg/mL, 10.9 ± 0.8 µg h/mL, and 0.07 ± 0.07 µg/mL, respectively [Absorption. After oral administration of COBI with food to HIV-1 infected subjects, peak, plasma concentrations were reached 4 h post-dose. Mean steady-state Cmax, AUC, and Cper-dose values  after administration of multiple doses of COBI to HIV-1 infected subjects  by CYP3A and (minor pathway) by CYP2D6 and is not subject to glucuronidation. After oral administration, 99% of the circulating radioactivity detected in plasma was due to unmodified COBI. Concentrates of metabolites are low in urine and feces and do not contribute to the CYP3A inhibitory activity of COBI .Clearance. After oral administration, 86% and 8.2% of the dose were found in feces and urine, respectively. The median elimination half-life of COBI after administration of Tybost (trade name) is approximately 3–4 h ,134.Pharmacotoxicology. Conventional studies on repeated dose toxicity, genotoxicity, and toxicity to reproduction and development have shown no risk to humans.Side effects. As common side effects can be highlighted the following: high blood sugar, increased appetite, insomnia, drowsiness, nightmares, headache, dizziness, altered taste, nausea, diarrhea, abdominal pain, bloating, flatulence, dry mouth, jaundice, eczema and itch; rare side effects include kidney stones ,136.DRV is the latest formulated PI  providinThe compound was licensed for marketing in the United States of America in 2006 and in 2007 in Europe. Since 2016, DRV is a treatment option for children over three years of age, adolescents, and naive adults, infected with HIV-1, but also for critical patients . Since iLow doses of RTV or COBI are used to increase DRV plasma level. It can also be used in prophylaxis. The administration is done once or twice a day, only according to a schedule established by the specialist. This regimen may include 800 mg of DRV and 150 mg of COBI, 800 mg of DRV and 100 mg of RTV (once daily). When given twice a day, 600 mg of DRV in combination with 150 mg COBI or 100 mg RTV should be taken .DRV is marketed as a 100 mg/mL oral suspension or as 75, 150, 300, or 600 mg film-coated tablets. In fixed doses, it is formulated with COBI (800 mg DRV/150 mg COBI). As with other ARVs, DRV does not cure HIV/AIDS .DRV is an inhibitor of dimerization and catalytic activity of HIV-1 protease, thus inhibiting proteolytic activity and subsequent replication of HIV-1. It also selectively inhibits the cleavage of Gag-Pol-encoded HIV polyproteins in virus-infected cells, preventing the formation of infectious mature viral particles .have not been previously treated with ART; and6/L. In deciding to start DRV treatment in these patients previously treated with ART, the administration should be guided by genotypic testing [have been previously treated with ART, have no DRV resistance mutations (DRV-RAMs) and have HIV-1 plasma RNA <100,000 copies/mL and CD4 + cell count ≥100 cells × 10 testing .In therapy, a low dose of RTV or COBI, in combination or not with other ARV medicines, should be used to treat patients infected with HIV-1, adult, adolescent, and pediatric patients over three years old and with body weight ≥10–15 kg ,149, whoAfter initiating treatment with DRV, patients are advised not to change the dose, dosage form, or discontinue treatment without talking to their healthcare professionals. The drug interaction profile of DRV depends on the use of RTV or COBI as a pharmacokinetic enhancer. Therefore, DRV may have different contraindications and recommendations for concomitant use depending on the use of RTV or COBI for potentiation .The efficacy and safety of DRV alone or in combination with potentiating drugs have been demonstrated in numerous studies ,155,156.If the affinity for wild-type strains is increased, species that have developed resistance to PIs are less sensitive to DRV, and ARV activity is compromised .The major complication of ART is the evolution of drug-resistant viral strain variants. This resistance occurs due to rapid viral replication. Most PIs select viral species with one or more specific mutations in the coding region that confer resistance. DRV appears to have a high genetic barrier against developing viral resistance in the case of wild-type virus as well as a large group of clinical isolates resistant to other PIs . FollowiAlthough structurally, DRV is similar to amprenavir, DRV has two intertwined tetrahydrofuran rings. This difference is important in the antiviral activity of DRV, because the bistetrafuran fragment reverses stereochemistry at the point that binds it to the rest of the molecule and allows additional interactions of DRV with ASP 29, a key amino acid of the HIV protease .Pharmacokinetic studies in which DRV was administered alone showed a bioavailability of 37%. In combination with RTV, a potent CYP3A inhibitor, the plasma concentration increased, the bioavailability reaching 82%. This demonstrates that DRV is sensitive to a presystemic metabolism or to an efflux effect or even to both. Potentiation drugs reduce these effects. According to CPR, DRV is primarily metabolized by CYP3A. RTV and COBI inhibit CYP3A, thereby significantly increasing plasma DRV concentrations ,169,170.DRV is rapidly absorbed after oral administration. The maximum plasma concentration in the presence of a low dose of RTV is generally reached within 2.5–4 h ,149. TheP-glycoprotein from intestinal epithelial cells may decrease oral absorption of PIs by mediating drug efflux. Low levels of intestinal absorption, together with CYP 450 activity, are major factors in the low bioavailability of DRV. The combination of a boosting drug inhibits both the action of CYP 450 and the efflux transport systems in the intestinal mucosa, thus improving the bioavailability of DRV ,149.DRV is strongly bound to plasma proteins in a proportion of approximately 95%, binding in particular to plasma α1-acid glycoprotein ,167. It In vitro experiments with human liver microsomes (HLM) indicated that DRV mainly undergoes oxidative metabolism. DRV is extensively metabolized by the hepatic system CYP 450 and almost exclusively by the CYP3A4 isoenzyme. In humans, at least three oxidative metabolites of DRV were identified, with 10-fold lower activity on the wild-type HIV than the parent substance ,161.A study conducted in 2009  demonstrAfter a dose of 400/100 mg, DRV with RTV, approximately 79.5 and 13.9% of the administered dose is found in the feces and urine, respectively. Unchanged DRV was approximately 41.2 and 7.7% of the administered dose in feces and urine, respectively. The terminal clearance half-life of DRV was approximately 15 h when combined with RTV. The intravenous clearance of DRV alone (150 mg) and in the presence of a low dose of RTV was 32.8 and 5.9 L/h, respectively ,149.DRV is generally well tolerated in humans. The most common side effect is rash 7% of cases. This is followed by diarrhea (2.3%), headache (3.8%), abdominal pain (2.3%), constipation (2.3%), and vomiting (1.5%). DRV can also cause allergic reactions, and people allergic to RTV can also have a reaction to DRV ,176. HigAs common side effects of DRV are as follows: diarrhea, vomiting, nausea, indigestion, eczema, itching, abdominal pain, bloating, flatulence, headache, fever, peripheral neuropathy, lipodystrophy, insomnia, weakness, fatigue, diabetes, increased creatinine levels, cholesterol, and liver enzymes. Rare side effects  may also occur. It must not be used in patients with severe hepatic impairment and should be used with caution in cases of moderate hepatic impairment. Drug–drug interactions are a permanent concern for clinicians treating HIV-infected patients. In addition to HAART, which requires combinations of multiple ARV drugs, patients should frequently take other medications to prevent or treat opportunistic infections, associated diseases, and to manage ARV side effects. Many of these drug interactions can lead to dose adjustments or even contraindications to their use . HoweverThe emergence of PIs was an important step in the treatment of HIV-infected patients. Their use, together with two nucleoside analogues, has radically changed, in a positive way, the life prognosis of patients. If the initially developed PIs had many side effects and thus imposed limitations in administration, recent generations are well tolerated, significantly improving the quality of life of the patients. Today, PIs have a convenient dosage, are administered in a single dose, daily, with high potency and a favorable safety profile. Co-administration of a pharmacokinetic enhancer has greatly contributed to this effective and safe therapeutic profile of PIs. To this, it is added the increased barrier to the occurrence of viral resistance of PIs and the specific immune benefit of this class. All these features make PIs key agents in the fight against HIV. Dual therapeutic regimens were initially designed to be administered to patients in whom monotherapy had failed. However, the practice has proved unquestionable qualities; in addition to the much higher potency, there has been better patient compliance due to the decrease in the pill burden and the reduction in the number and intensity of side effects.DRV is part of the new generation of PIs, bringing a great advantage in the treatment of HIV/AIDS because it has superior efficacy on wild-type HIV but also on already resistant strains. DRV co-administered with a booster—RTV or COBI—has a higher pharmacokinetic profile due to booster inhibition of metabolic pathways. Boosted DRV is well tolerated by patients, with fewer side effects than other regimens. Therefore, DRV co-administered with RTV or COBI is a viable treatment option for both naive and experienced patients.COBI and RTV are considered equivalent pharmacokinetic stimulants with similar inhibitory effects on CYP3A4, CYP2D6, P-gp, and other transporters. Similar exposures to elvitegravir, atazanavir, and DRV are made when combined with either substance. However, in the presence of inducers, etravirine, rifamycin, or anticonvulsants, COBI may not be as effective as RTV in inhibiting CYP3A4. However, COBI is a more specific inhibitor of CYP3A than RTV and has no inducing properties. Thus, it is anticipated that drugs metabolized primarily by CYP1A2, CYP2B6, CYP2C8, CYP2C9, and CYP2C19 or subject to glucuronidation reactions will be affected differently by RTV and COBI. Additionally, data on drug–drug pharmacokinetic interactions for COBI are often extrapolated from RTV. However, separate studies are needed in the case of COBI. Although they have similar profiles, problems can also occur when changing a treatment regimen that contains RTV with another that includes COBI. Clinicians need to know the differences in the pharmacokinetic profile of the two boosters, especially when evaluating and managing potential drug interactions, with most HIV+ patients having multiple comorbidities and co-medications. In these situations, monitoring the therapy, by various means, is absolutely necessary in order to be able to act promptly by adjusting the doses or by modifying the therapeutic regimens.


Immune reconstitution failure after HIV treatment is a multifactorial phenomenon that may also be associated with a single polymorphism of human leukocyte antigen (HLA); however, few reports include patients from the Brazilian Amazon. Our objective was to evaluate the association of the immunogenic profile of the “classical” HLA-I and HLA-II loci with treatment nonresponse in a regional cohort monitored over 24 months since HIV diagnosis.+/CD8+ T lymphocyte quantification was performed by immunophenotyping and flow cytometry . Infection was monitored via test and logistics platforms (SISCEL and SICLOM). Therapeutic response failure was inferred based on CD4+ T lymphocyte quantification after 1 year of therapy. Loci A, B and DRB1 were genotyped using PCR-SSO . Statistical tests were applied using GENEPOP, GraphPad Prism 8.4.3 and BioEstat 5.3.Treatment-free participants from reference centers in the state of Pará, Brazil, were enrolled. Infection screening was performed using enzyme immunoassays  and confirmed by immunoblots . Plasma viral load was quantified by real-time PCR . CD4+ ≥ 500 cells/µL), and 136 did not respond to treatment (CD4+ < 500 cells/µL). The allele frequencies of the loci were similar to heterogeneous populations. The allelic profile of locus B was statistically associated with treatment nonresponse, and the B*13, B*35 and B*39 alleles had the greatest probabilistic influence. The B*13 allele had the highest risk of treatment nonresponse, and carriers of the allele had a detectable viral load and a CD4+ T lymphocyte count less than 400 cells/µL with up to 2 years of therapy. The B*13 allele was associated with a switch in treatment regimens, preferably to efavirenz (EFZ)-based regimens, and among those who switched regimens, half had a history of coinfection with tuberculosis.Of the 270 patients monitored, 134 responded to treatment  from a heterogeneous population in the Brazilian Amazon. In tion ART . In a sitoxicity .Other class 1 and class 2 molecules are abnormally expressed in patients receiving ART, each related to an aspect of the immune response , 28. It In this context, we observed a lack of studies on the relationship between HLA and treatment nonresponse in patients from the Brazilian Amazon and the northern region of Brazil. In Brazil, the frequency of nonresponders tends to vary from 38 to 50% depending on the region and on the methodology used in studies, in which biomarkers of varying etiology have been associated with the observed immunological condition –33.Thus, herein, we evaluate the frequency and possible associations of HLA class 1 (HLA-A and HLA-B) and class 2 (HLA-DRB1) alleles in nonresponder PLHIVs from a northern Brazilian cohort.Setor de Atendimento Médico Unificado do Instituto Evandro Chagas  and Centro de Atenção à Saúde nas Doenças Infecciosas Adquiridas  through the weekly selection of peripheral blood samples from prescreened PLHIV or suspected HIV-infected people living in the state of Pará, Brazil, from January 2018 to January 2019.This cohort study was created by recruiting patients from Instituto Evandro Chagas . All participants were informed about the study objectives, and those who agreed to participate signed an informed consent form and answered a sociodemographic questionnaire. Individuals under 18 years of age or who were already receiving ART when first approached were not considered for the study. Participants who died, those who did not have continuous data on monitoring platforms, or those who abandoned the governmental assistance program for PLHIV during the study period were excluded.In compliance with resolutions 466/2012 and 347/05 of the National Health Council, which addresses the guidelines and regulatory standards of research involving human beings, the project was submitted for ethical review and approved by the Human Research Ethics Committee of The suspicion of HIV infection was confirmed by the qualitative detection of p24 antigen and anti-HIV-1 and anti-HIV-2 IgG antibodies by enzyme immunoassays . Serology was confirmed using a rapid Immunoblot DPP HIV-1/2 kit  following the manufacturer’s protocol.Plasma HIV viral load was quantified by real-time PCR using an Abbott mSample Preparation System RNA extraction kit and Abbott Real-Time HIV-1 amplification matrix .high CD3+ CD4+ CD8-) and CD8 T (CD45high CD3+ CD4- CD8+) lymphocytes was performed by immunophenotyping and flow cytometry using BD FACSCalibur-4 core equipment, FACSCount™ Reagents and Tritest™/TruCount kits .The quantification of CD4 T  every six months. The quantification methods in each period were the same as previously described. The data regarding the management and distribution of antiretrovirals were obtained from Sistema de Controle Logístico de Medicamentos  every six months; the initial therapeutic regimens, changes in approach and reasons for changes were determined. The data collection occurred for twenty-four months from the date of inclusion in the study.Lymphocyte quantification and viral load data, after the first collection, were obtained from + < 500 cells/µL; varied viral load) and treatment responders . We chose this cutoff because a previous analysis showed that for the same period, the viral load itself was not a determining factor in the differentiation of different progression groups. These established groups were evaluated for another year of therapy, totaling 24 months of analysis and data collection.In total, 270 PLHIVs participated in the study; after one year of ART, these PLHIVs were stratified based on their immune response to treatment into treatment nonresponders  following the manufacturer’s recommendations. The newly extracted DNA samples were quantified using a Qubit spectrofluorometer , following the manufacturer’s recommendations; and the degree of purity was evaluated using a NanoDrop™ 2000/2000c spectrophotometer , in which the elution solution used in the extraction of genetic material was used as a reference standard.We standardized the following profiles as the ideal range for successful amplification: for loci A and DRB1, a concentration between 10 and 15 µg/ml; for the B locus, a concentration between 10 and 12 µg/mL. The degree of purity for all loci was represented by the ratios 260/280: 1.8-2.0 and 260/230: 1.8-2.2. Samples having concentrations above the established standard were diluted in DNase/RNase-free ultrapure distilled water . Samples with concentrations below the established standard were reextracted, and those that still had an inadequate profile were discarded from subsequent analyses.In this sense, of the 270 participants obtained, we were not successful in genotyping some samples, of which only one sample from the responder group was not genotyped for locus A. For locus B, 29 samples from the responder group and 31 samples from the nonresponder group were not genotyped. For the DRB1 locus, only three samples were not genotyped from the nonresponder group.via PCR-SSO (polymerase chain reaction-sequence specific oligonucleotide) methodology using Luminex technology  and a LABType® kit .Loci A, B and DRB1 of HLA classes 1 and 2 were genotyped ® Thermal Cycler, following the amplification protocol described in the kit. To confirm the amplification, 2.5% agarose gel electrophoresis was performed.In the amplification step, the target DNA was amplified by conventional PCR in a reaction mixture containing specific primers for each locus provided by the kit, recombinant Taq  and D-mix solution provided in the kit. Amplification occurred in a MastercyclerIn the hybridization stage, the amplified DNA was denatured and hybridized with a set of specific oligonucleotide probes, which were immobilized in fluorescently labelled polystyrene microspheres. After the hybridization step, the microspheres were washed and subsequently incubated with a streptavidin-phycoerythrin conjugate (SAPE), which binds to biotinylated amplified DNA.In the last phase, a Luminex analyzer was used to measure the intensity of phycoerythrin fluorescence in each microsphere, and the data generated were stored to specific extensions. From those data, HLA Fusion software was used to determine the alleles of the HLA genes. The pattern of reactivity of each DNA sample relative to the set of probes conjugated to the microspheres allowed the establishment of the HLA genotype at medium resolution.To corroborate the proposed groupings, we applied discriminant multivariate analysis that adopted the same definition criteria for the groups of nonresponders and responders; a scatter plot was inferred for group identification.We applied Cochran’s Q test in the paired comparisons of lymphocyte quantification and viral load data obtained during the study; for intergroup analyses, we applied the Kruskal–Wallis test. We chose nonparametric tests due to the degree of normality of the variables studied, as estimated by the Lilliefors test.For each HLA locus, Hardy-Weinberg equilibrium was measured, selecting as an alternative hypothesis of interest the excess heterozygotes in the groups; the standard parameters of the Markov chain were adopted. The genotypic linkage disequilibrium between the loci was determined by the log probability ratio, also adopting the Markov standard parameters. Allele clusters Bw4 and Bw6 were identified based on the HLA nomenclature database .The parametric proportion (π) of the most frequent allele of each locus was calculated to estimate the confidence interval of the expected global frequency. We applied multivariate cluster analysis to cluster the populations of different ethnic profiles based on allele frequency data available in the “The Allele Frequency Net Database” . The allHe) for each HLA locus in the studied population was calculated based on the formula adapted from Nei et al.  to compare the proposed curves. We adopted the proportion of responders to ART as an event of interest in the analysis the 24-month study period as the time variant. The estimates of response to therapy were evaluated among the alleles associated with the response progression profile.We calculated the Spearman coefficient using a general correlation matrix for all the genetic, immunological, virological and therapeutic factors evaluated. The correlations were categorized as follows: negative and strong when the Spearman coefficient was between -1.0 and -0.5; negative and weak when the Spearman coefficient was between -0.5 and 0; positive and weak when the Spearman coefficient was between 0 and 0.5; and positive and strong when the Spearman coefficient was between 0.5 and 1.0.For the statistical analyses, we adopted a significance level (α) of 95%, considering a probability of significance (p) less than or equal to 0.05 as a criterion for rejecting the null hypotheses. The estimation of Hardy-Weinberg equilibrium and linkage disequilibrium were calculated in GENEPOP software . The oth10 (p< 0.0001), a significant reduction in CD8+ T lymphocyte count (p< 0.0001), and an absolute increase in CD4+ T lymphocytes (p< 0.0001) after starting ART, over 24 months of observations . The multivariate analysis clearly showed that responders and nonresponders formed two distinct groups with unique immunological characteristics that did not overlap , and 136 manifested failures in the restoration of CD410 remained significantly detectable in nonresponders up to 12 months after initiating ART  (+ T lymphocyte count in nonresponders remained less than 500 cells/µL regardless of their time receiving ART  (+ T lymphocyte count to be higher in nonresponders up to the first 12 months after initiating ART  : 1.94 (1.06-3.54)], those with low education levels  and heterosexual individuals  had an approximately two times higher risk of nonresponse to ART and that an active sex life was a more frequent factor in responders . A switch in treatment was the most prominent factor in the first analysis, being approximately 10 times more likely to occur in patients with immune failure after ART  Table 2.Based on the multiple logistic regression results, sexual preference [OR (95% CI): 1.70 (1.00-2.89)] and switch in therapy [OR (95% CI): 6.42 (2.12-19.39)] were the factors that remained associated with response failure Table 2.He: 0.93) ; for locus B, the B*35 allele was the most common ; and for the DRB1 locus, the DRB1*13 allele was the most common . The expected heterozygosity was highest for locus B  were similar to those observed in heterogeneous ethnic populations from different regions of Brazil, more specifically from northern Brazil. The allele frequency for Caucasoids was directly related to the heterogeneous clade; in another segment, we observed a closer relationship between Amerindians and Asians; and Negroes were related to this clade at the second level ;  Figure 32 = 9.923; p = 0.0192); the B*13 allele had the lowest proportion of ART responders across the study period, with approximately 6.67% of responders at the end of 24 months of analysis, followed by the B*35 allele (16.15%), B* 39 (19.93%) and other alleles (24.05%) : 1.86 (1.08-3.18)] and threefold for the B*39 allele [OR (95% CI): 3.33 (1.33-8.69)]; the B*13 allele, with the highest ratio, had an odds ratio for nonresponse approximately fourfold higher [OR (95% CI): 4.06 (0.45-36.62)]. We suggest that the extensive confidence interval is a reflection of the low allele frequency in the groups , (month 6 = p: 0.017), (month 12 = p: 0.0032)]. After 12 months of ART, the lymphocyte count was standardized among the alleles; however, the carriers of the B*13 allele had low counts relative to the others  and carriers of alleles without a response risk (p< 0.0001) over the 24 months of therapy  increase in the rate of regimen switching among carriers of the B*13 allele and a 25% decrease (1 to 4) in the rates of maintaining and continuing previous regimens , and only 25% started treatment with the second most common regimen: tenofovir + lamivudine + efavirenz (TDF+3TC+EFZ). However, after 24 months of therapy, we observed an inversion of prevalence, with the TDF+3TC+EFZ regimen becoming the most common (50%); the TDF+3TC and DTG regimen was maintained for 25% of patients, and a new regimen, raltegravir and tenofovir + lamivudine (RAL and TDF+3TC), was administered to 25% of patients (p: 0.9124) (The reasons for switching therapy were not reported for most patients (50-90%); approximately 66% of carriers of the B*13 allele switched due to coinfection with tuberculosis, and approximately 5% of carriers of the B*35 allele switched therapy due to adverse reactions to the previous regimen. Pregnancy (15%), use of metformin as an antidiabetic agent (4%) and virological failure (4%) were reported only for carriers of other alleles. The frequency of the reasons for switching was not significant among the alleles : 8.27; We generated a correlation matrix for the genetic, immunological and therapeutic factors evaluated in the present study Figure 6p: 0.0210), the TDF+3TC+EFZ regimen , a low CD4+ T lymphocyte count  and increased plasma viral load . The B*35 allele was not correlated with the factors evaluated. The B*39 allele was correlated with an increased viral load , a low CD4+ T lymphocyte count  and a high CD8+ T lymphocyte count .The B*13 allele was significantly correlated with switching therapy  and TDF+3TC+EFZ . The maintenance of the CD4+ T lymphocyte count was correlated only with the TDF+3TC and DTG regimen . A reduction in CD8+ T lymphocyte count was correlated with the TDF+3TC+EFZ regimen . Most patients administered the RAL+TDF+3TC  and AZT+ 3TC+EFZ  regimens switched therapy during the two years of treatment. The TDF+3TC and DTG  and TDF+3TC+EFZ  regimens were correlated with maintaining the same regimen throughout the two years of treatment.The therapeutic regimens significantly correlated with reductions in viral load were TDF+3TC and DTG , 3TC+TDF, and the integrase inhibitor (INI) DTG . Users oresponse ; it is aresponse  that canresponse . The addresponse .+ T lymphocyte count.However, the exception to this preferred regimen is coinfection with tuberculosis, for which the administration of a nonnucleoside reverse transcriptase inhibitor (NNRTI), EFZ, is indicated as a substitute for DTG  because Studies have discussed the association of the B*13 allele with the risk of developing thoracic tuberculosis and multisystemic sarcoidosis , 67. Int+ T count, regardless of virological status . The patients/participants provided their written informed consent to participate in this study.TAFM, OM, RCMS, FBF, IBC, and ACRV were the creators of the project. LMSP, ESF, ABCF, and FLPR were responsible for sample collection at reference centers. LMSP, ESF and IrBC developed the methodology for the project; specifically, EVOJ and PJSMM conducted the HLA loci genotyping. LMSP conducted the statistical analysis and wrote the article. ESF, FBF, IgBC, and ACRV reviewed the article. All authors contributed to the article and approved the submitted version.Secretaria de Vigilância em Saúde do Ministério da Saúde , Conselho Nacional de Desenvolvimento Científico e Tecnológico  (no. 301869/2017-0) and Fundação Amazônia de Amparo a Estudos e Pesquisa – FAPESPA (ICAAF-60/2020). We thank Coordenação de Aperfeiçoamento de Pessoal de Nível Superior  for granting a scholarship (process number: 88882.183970/2018-01).This study was funded by specific incentives from The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors and the reviewers. Any product that may be evaluated in this article, or claim that may be made by its manufacturer, is not guaranteed or endorsed by the publisher.


Tuberculosis (TB) remains a public health problem, particularly in people living with human immunodeficiency virus (PLHIV). Yet, efforts to reduce TB incidence using isoniazid preventive therapy (IPT) have been curtailed by poor uptake of this intervention. This study reviewed the rate of IPT initiation in the sub-Saharan country of Lesotho, which has one of the highest TB incidences in the world.Time to IPT initiation in randomly sampled medical records of PLHIV was analysed using Cox’s proportional hazards regression. Differences in the periods of enrolment into Human immunodeficiency virus (HIV) care were controlled for by considering the year IPT was launched (2011) as the base year and stratifying the medical records into the 2004–2010 cohort (before the launch of IPT) and the 2011–2016 cohort (after the launch).p < 0.05) higher rate of initiation . Age group, district category and duration of antiretroviral therapy emerged as the most significant predictors of IPT initiation, while district category and gender significantly predicted IPT therapy interruption.Out of 2955 patients included in the final analysis, 68.8% had received IPT by the study exit time. However, the overall rate of IPT initiation was 20.6 per 100 person-years, with 135 (6.6%) treatment interruptions. Compared to the 2004–2010 cohort, the 2011–2016 had a significantly (These findings indicate a high uptake of IPT with a slow rate of implementation. Significant factors associated with disparities in the initiation and interruption of IPT therapy in this study are important for policy review. Despite the considerable effectiveness of isoniazid preventive therapy (IPT), recommended by the WHO2 for the prevention of TB in people living with HIV (PLHIV), the rates of initiation and retention on IPT have generally been suboptimal,6 thus necessitating more population studies of this intervention.Human immunodeficiency virus (HIV) and tuberculosis (TB) have become a global syndemic responsible for nearly 25% of all HIV-associated deaths.10 Some countries were not convinced of the benefits of IPT and deferred the implementation of IPT altogether for many years. For example, the Ivory Coast had not implemented IPT by 2014.11The reasons for the slow implementation vary by country, with the most cited being poor health care delivery systems, underestimation of potential public health impact of IPT by HIV/TB programme managers and a lack of adequate means to exclude a pre-existing TB infection prior to treatment initiation, among others.12 Scholars believe that this can be overcome by closing the ‘know-do gap’, that is, the gap between what is known and what gets implemented.15 Further, Pablos-Mendez and Shademani15 note that slow IPT uptake in developing countries may be a symptom of a range of problems in the health systems of these countries, including a lack of evaluation studies. Therefore, the evaluation of IPT uptake is a crucial step to improving the implementation of IPT.The uptake of health interventions, particularly in developing countries, is often slow.16 With a 23.5% adult HIV prevalence rate, the country has the second highest prevalence rate of HIV worldwide17 and with 665 TB incidences per 100 000 population,1 the country is one of the top three nations with the highest rates of TB worldwide.Lesotho is an independent country completely surrounded by South Africa, with about 2.2 million people and an estimated gross domestic product (GDP) per capita of $1000.00, which puts the country into the low-income countries tier.18 However, ever since its launch, information on the rate of initiation of IPT and the associated factors has remained obscure.18 Of note, the country has not provided data for the IPT indicator to the WHO repository from the time the programme was launched.1 So, this study assessed the rate of initiation and retention of PLHIV on IPT and the associated factors in the high HIV/TB burden setting of Lesotho with the aim of identifying the barriers to the implementation of IPT in the country.The Government of Lesotho (GoL) implemented the 6-month IPT guidelines of the WHO in 2011.19Lesotho is divided into 10 administrative districts, five of which are densely populated and are considered scale-up districts for HIV/TB programmes. The scale-up districts occupy the lowlands of the country, while the other five  occupy the mountainous sparsely populated highlands.Study participants were sampled from three district hospitals in three sparsely populated  districts and five district hospitals from three densely inhabited  districts of the country see .4This longitudinal retrospective cohort study analysed, based on Cox’s proportional hazard regression, the probability of IPT initiation in PLHIV in Lesotho, considering time to IPT as the dependent variable. Further, the study assumed that the rate of IPT initiation was fairly constant and that the rate generally fitted an exponential curve that could be modelled by Cox’s proportional hazards function.The target population was PLHIV enrolled into HIV care between 2004 and 2016 in the eight health institutions, all of which were district hospitals with at least 2000 patients on antiretroviral therapy (ART). Antiretroviral therapy records of HIV-positive children, adolescents and adults, including geriatric patients and pregnant women, were selected using stratified systematic random sampling across eight health facilities, ensuring proportional representation of all patient categories including gender, age and period of enrolment.20 The minimum number of patients’ records, assuming a relative precision of 10% at 5% significance level,20 was 385 at each hospital or 3080 in the eight hospitals. However, an additional 40% were added to cater for incomplete records, implying that at least 4620 patient files were required.The minimum sample size was calculated following standard guidelines for estimating incidence with a specified relative precision.File selection was based on stratified systematic random sampling using a sampling frame that was prepared from the ART attendance registers by drawing a list of all the patients enrolled into HIV care since 2004. The total sample of files per hospital was obtained by dividing the total number of patients enrolled in HIV care by the proportional target sample size for the hospital.Demographic and clinical data were captured between January and October 2016 from the paper-based ART and IPT registers into a Microsoft Access database  designed by the researchers. Overall, 4122 patient files were collected. Of the 4122 patients, 1167 were excluded according to the exclusion criteria presented in Time-variant variables such as age were calculated according to the time at enrolment into HIV care. Patients late for their scheduled appointments by more than a month and those who did not return for ART services were classified as loss to follow-up.Time to IPT (in months) was calculated by subtracting the date of enrolment into HIV care from the date IPT was prescribed. Patient treatment outcomes were assessed by median cluster of differentiation 4 (CD4) and viral load values. The duration before ART commencement (in years), known as the pre-ART period, was calculated by subtracting the date of HIV diagnosis from that of ART commencement. Furthermore, the proportion of patients who had interrupted IPT therapy was also calculated and the factors associated with interrupting therapy were assessed using chi-square test and logistic regression analysis.Data for IPT initiation in the database were verified and exported to Stata version 13.1  for further cleaning and analysis. Data were formatted for survival analysis as discrete-time survival data with interval date as the time variable. The occurrence of the IPT event defined the ‘failure’ outcome with the time scale in years. To obtain comparable follow-up times, patients enrolled before IPT was available were declared to have entered the risk set in 2011, the year IPT was launched in the country. For purposes of calculating Cox’s proportional hazards ratios, entry times into the risk set for all the patients were delayed by 1 month to calibrate for inconsistencies at first entry into the risk set. The date of enrolment into HIV care and the exit date marked the left and right censoring times, respectively.21 in this study was the probability that an individual with certain characteristics would receive IPT in a specified time. To cater for observation gaps, follow-up times were subdivided into 6-month discrete intervals22 and Breslow’s correction was used to correct for this treatment of data.21The proportional ‘hazard’p < 0.2 were included in the IPT initiation model.Patient characteristics associated with IPT initiation were summarised by cross-tabulation. These characteristics were further analysed using univariate Kaplan–Meier survival functions to determine their suitability in the analysis model. Further, Wilcoxon’s log-rank test and Cox regression analysis were used to determine equality across strata for categorical variables and continuous variables, respectively. Predictors with The year 2011, when IPT was launched, was set as the base year for follow-up and medical records were stratified into the 2004–2010 cohort (before the launch of IPT) and the 2011–2016 cohort (after the launch of IPT). Ten predictors see  were selp < 0.005). The models with and without the interaction variables were compared using the likelihood ratio test (Lrtest) and the difference was found to be significant , implying that the bigger model with the interaction terms was superior to the one without.The model was tested for predictor interaction and two variables namely, duration of ART and the district category had significant interactions (p = 0.032), violated the proportionality assumption, but was, however, retained in the model and the anomaly corrected through stratification with period of enrolment.The unstratified model was checked for proportionality using the Schoenfeld and scaled Schoenfeld residuals (Phtest) test. One categorical variable, duration of ART significantly  higher initiation rate .In total, 2955 patients were included in the final analysis (see p < 0.300) with IPT initiation in the patients enrolled on ART before 2011. However, for the patients enrolled on ART after 2011, more variables, namely, gender, age, district category, adherence, baseline WHO clinical stage, duration on pre-ART and duration on ART had substantial influence (p < 0.300) on IPT initiation.Four variables, namely gender, antiretroviral treatment failure, baseline WHO clinical stage and duration on ART, had considerable association (p < 0.2) categorical predictor variables that had distinct plots were namely: (1) gender, (2) marital status, (3) district, (4) geographic location, (5) period of enrolment into HIV care, (6) baseline WHO clinical stage, (7) adherence to ART, (8) patient status at exit time of the study and (9) history of past TB infection on first visit. For continuous predictors, significant (p < 0.2) predictors  associated with interrupting IPT by chi-square test, while baseline CD4 count was only marginally significant . Multiple logistic regression analysis revealed that although baseline CD4 count category 351 cells/mm3 – 500 cells/mm3  and baseline WHO clinical stage IV  were also significant, sparsely populated district category  and gender  were the most influential in determining interruption of IPT therapy.p < 0.050) predictors (p = 0.000) interactions  adults had 78% higher probability of receiving IPT  in relation to children and adolescents; (2) patients in the densely populated districts had 59% lower likelihood of receiving IPT  compared to the sparsely populated districts and (3) longer durations on ART were still associated with higher chances of IPT initiation. For instance, patients on ART for 5 or more years were 33% more likely to receive IPT compared to patients on ART for less than 5 years . However, comparing two subjects on ART for 5 or more years in the densely populated districts and taking into account the interaction terms, having 5 or more years of ART was 34% more likely to receive IPT compared to patients on ART for less than 5 years.-years. This indicates that despite the majority of PLHIV getting initiated on IPT, the rate of IPT implementation remains slow. More importantly, this study also indicates the need for reporting the rate of initiation for IPT in addition to national coverage statistics as is the current practice globally. Currently, data on rate IPT initiation are scarce, with only Brazil reporting such data – the rate of initiation in that country was 20.0 per 100 person-years in 2014.4 Widespread tracking of the rate of initiation for IPT in developing countries would certainly need more bioinformatic tools and skills that are often lacking in these countries.The study found a high IPT uptake (68.8%) with generally a slow IPT initiation rate of 20.6 per 100 person1 reports that national coverage for IPT in 15 of the 30 high HIV/TB burden countries ranged from 1% in Swaziland to 53% in South Africa. Other countries in sub-Saharan Africa with IPT coverage higher than 30% include Ethiopia (45%), Nigeria (39%), Sierra Leone (22%), Zambia (18%), Namibia (15%) and Angola (13%). Notably, IPT coverage in many sub-Saharan countries, such as Botswana, Malawi, Ghana and Uganda, was unknown in 2017.1 Therefore, considering the high TB burden in Lesotho, there is need to maintain the high uptake rate for IPT while improving the slow rate of initiation to ensure that newly ART-initiated patients are given IPT as early as possible.23Despite the lack of comparable data on the rate of IPT initiation from other countries in the southern African region and beyond, IPT coverage in Lesotho is commendable and encouraging. To put IPT coverage for Lesotho into perspective, WHO24 this study further highlights that Lesotho is losing the opportunity to control TB through IPT. With an incidence rate of TB exceeding 600 cases/100 000 population,24 Lesotho needs to intensify the scaling up of IPT.Given that IPT is projected to be more effective in high TB burden countries when optimally implemented,The median time to IPT for the 2004–2010 cohort was almost twice as high as that of the 2011–2016 cohort, implying that the patients enrolled on ART after IPT was launched have a higher initiation rate in this setting. This disparity therefore needs to be addressed.7 and Triasih et al.25 in Ethiopia and Indonesia, respectively, note that children in resource-limited high TB burden settings have a low initiation rate of IPT despite that a 6-month course of IPT reduces the risk of childhood TB by the same margin of about 60% as adults. Lesotho therefore needs to scale-up TB contact screening as recommended by WHO.23 Deficiencies for the identification of children in need of IPT have also been reported in Brazil, Benin and Indonesia,27 and these include health care worker and health facility-related factors, including social support and access.The fact that children and adolescents had a lower chance of IPT initiation compared to adults in both the 2004–2010 and 2011–2016 cohorts emphasises the need for scale-up efforts for these patient groups. Tadesse et al.19 The lower initiation rates in the densely populated districts indicate that IPT scale-up efforts, currently supported by President’s Emergency Plan for AIDS Relief (PEPFAR) Lesotho, 19 need to be intensified in these districts.Isoniazid preventive therapy initiation in the densely populated districts was much lower in the 2011–2016 cohort. Access to HIV/TB services including IPT in the densely populated districts has generally been slow because of a number of reasons including resource limitations for scale-up efforts in these areas that have an estimated 72% of the country’s population.3 – 500 cells/mm3 and baseline WHO clinical stage IV. Patients in the sparsely populated districts, particularly those who are bedridden and in WHO clinical stage IV, may be interrupting therapy because of long distances from the hospitals and the mountainous terrain associated with these geographic locations. Scaling up health care delivery in these areas is therefore needed to reduce therapy interruption. In South Africa, inefficient health service delivery, ineffective communication with health care workers and the financial burden of transport to clinic were the most significant factors for interrupting IPT therapy.28 Higher rates of treatment interruption among men emphasise the need for intensified patient education in this group. In Botswana, men also had more interrupted IPT therapy than women.29Interrupting of IPT therapy in this study was associated with staying in the sparsely populated districts, being male, having baseline CD4 count of 351 cells/mm30 Therefore, there is a need to assess the effect of health care worker factors on implementation of IPT in Lesotho.A qualitative assessment of the factors contributing to low IPT initiation is required in this setting. Of note, barriers to IPT implementation in other settings include health care worker inexperience, unawareness of the benefits of IPT, as well as poor understanding of IPT guidelines and TB screening tools.11 This highlights the magnitude of the challenge of scaling up this intervention in developing countries.Of note, in some African countries such as the Ivory Coast, the national guidelines had not started using IPT by 2014, citing that IPT could lead to resistant TB bacilli in patients with undiagnosed TB.12 note, interventions must factor in the preferences of the intended target populations to improve initiation and adherence to the intervention. Therefore, investigations on patient preferences and concerns about IPT are needed in Lesotho. However, the main strength of this study is the reporting of IPT initiation in person-years which allows comparisons with other settings outside Lesotho. This study also demonstrates that routine data in ART programmes of developing countries can be useful for inferential analysis.This study is not without limitations, one of which is the lack of data on patient views. As Ostermann et al.This study investigated the rate of IPT initiation from the time the IPT programme was launched in 2011 in a high TB burden setting of Lesotho. Despite the high overall IPT uptake, the rate of IPT initiation was slow. The slow initiation of IPT is disconcerting and the factors associated with poor rate of initiation in this study need to be addressed. The high rate of IPT treatment interruption in the sparsely inhabited districts is evidence to the need to improve the monitoring of this programme. Clearly, the implementation of this health intervention in a high TB burden setting of Lesotho needs further scale-up.