the treatment of hepatitis c virus ( hcv ) infection has evolved from peginterferon alfa ( pegifn ) plus ribavirin ( rbv)based regimens to combinations of alloral , directacting antivirals ( daa ) , including daclatasvir  a pangenotypic ns5a inhibitor ( hcv genotypes 16 in vitro )  and the ns3 protease inhibitor , asunaprevir ( active against hcv genotypes 1 , 4 , 5 , and 6 in vitro ) . the efficacy and safety of daclatasvir and asunaprevir in combination has been assessed in multiple phase 3 studies , including the multicohort hallmarkdual study in treatmentnaive and pegifn / rbvineligible / intolerant hcv genotype 1binfected patients from 18 countries , including israel 1 . the sustained virologic response rate at posttreatment week 12 ( svr12 ) in the overall population of hallmarkdual following treatment with daclatasvir 60 mg once daily in combination with asunaprevir 100 mg twice daily administered orally for 24 weeks was 84% ( 542/643 ) and a comparable rate in patients from israel was observed ( overall , 82% [ 9/11 ] ; prior null responders , 3/3 ; pegifn / rbv ineligible / intolerant , 6/8 ) .
svr12 rates were enhanced in patients without ns5a resistanceassociated variants ( ravs ; l31 and/or y93 ) in both the overall population ( 92% ) and patients from israel ( 7/8 ) , and agree with similar findings from a pooled analysis of five studies in hcv genotype 1b infection 2 .
among the patients from hallmarkdual ( ai447028 ; clinicaltrials.gov number nct01581203 ) who did not achieve svr12 was a cirrhotic 58yearold caucasian female from israel who had a null response to prior pegifn / rbv therapy and was ineligible for retreatment with pegifn / rbv for reasons of anemia and neutropenia .
the patient had hcv rna at baseline of log10 5.43 iu / ml , no baseline ns5a or ns3 ravs shown to result in resistance to daclatasvir or asunaprevir , and 100% compliance with respect to daclatasvir and asunaprevir dosing and treatment duration .
pretreatment clinical laboratory abnormalities were graded according to division of aids criteria v1.0 . prior to initiating therapy with daclatasvir and asunaprevir , grade 3 elevations in total bilirubin
were observed from pretreatment through ontreatment week 2 , with subsequent fluctuations between grades 12 from week 4 to resolution at followup week 4 .
elevations in direct bilirubin were also observed from pretreatment ( 9.6  upper limit of normal [ uln ] ) that decreased or remained consistent at all ontreatment assessments ( week 2 , 7.0  uln ; end of treatment , 3.3  uln ) and at followup week 4 ( 3.0  uln ) . a pretreatment grade 2 aspartate aminotransferase elevation resolved by week 2 , and a subsequent grade 1 elevation during week 4 resolved by week 6 . a pretreatment grade 1 alanine aminotransferase elevation resolved prior to the initiation of therapy .
alkaline phosphatase levels were elevated ( grade 1 ) from pretreatment until followup week 4 . during treatment with daclatasvir and asunaprevir ,
the patient experienced rapid viral decline and achieved detectable levels of hcv rna below the lower limit of quantification ( 25 iu / ml ) at week 4 .
the patient then had undetectable hcv rna at week 6 that remained undetectable until relapse occurred at posttreatment week 12 ( hcv rna was assessed at ontreatment weeks 1 , 2 , 4 , 6 , 8 , 10 , and 12 ; and posttreatment weeks 4 , 12 , and 24 ) ; hcv rna at posttreatment week 12 was log10 6.2 iu / ml ( fig .
1 ) . viral decline during initial treatment ( daclatasvir plus asunaprevir ) and retreatment ( sofosbuvir plus simeprevir ) .
initial treatment with daclatasvir and asunaprevir for 24 weeks ; retreatment with sofosbuvir and simeprevir for 12 weeks .
bl , baseline ; eot , end of treatment ; fu , followup week ; hcv , hepatitis c virus .
populationbased sequencing of the patientderived hcv ns5a region from plasma samples collected at followup week 12 revealed the emergence of signature ravs in ns5a ( l31 m , y93h [ with baseline polymorphisms r30q and p58s ] ) and ns3 ( d168v ) ; these substitutions confer 44,000 and 357fold resistance to daclatasvir and asunaprevir in vitro , respectively . at followup week 24 ( last available sample for testing ) ,
these ravs were still present . on july 15 , 2014 , approximately 6 months after initial treatment relapse , the patient was retreated with sofosbuvir 400 mg once daily administered in combination with simeprevir 150 mg once daily administered orally for 12 weeks .
an assessment of ravs prior to retreatment was not conducted because plasma samples were not available .
sofosbuvir and simeprevir is a combination therapy that is equipotent in wildtype hcv replicons representative of hcv genotype 1b and variants with signature ns5a ( l31 m , y93h ) and ns3 ( d168v ) ravs 3 .
retreatment baseline hcv rna was log10 5.39 iu / ml . retreatment with sofosbuvir in combination with simeprevir resulted in a rapid viral decline ( detectable hcv rna below the lower limit of quantification at week 2 ) that resulted in undetectable hcv rna at retreatment week 4 .
the patient experienced an adverse event of mild rash between retreatment weeks 4 and 6 that resolved without sequelae .
grade 3 elevations in total bilirubin were observed during retreatment weeks 4 , 10 , and 12 ; a grade 2 elevation was observed during postretreatment week 6 .
elevations above the uln of direct bilirubin were observed during treatment weeks 4 ( 3.9  uln ) , 10 ( 4.4  uln ) , 12 ( 3.6  uln ) , and postretreatment week 6 ( 2.7  uln ) .
alanine and aspartate aminotransferase levels remained within normal limits through the treatment and followup periods .
elevations in thyroidstimulating hormone were also observed during treatment week 4 ( 1.2  uln ) , at end of retreatment ( 1.4  uln ) , and during postretreatment week 6 ( 1.6  uln ) .
overall , treatment with daclatasvir plus asunaprevir in the hallmarkdual study achieved high rates of svr12 in hcv genotype 1binfected patients without ns5a ravs and with or without ns3 ravs at baseline .
this case demonstrates that in the infrequent cases of virologic failure , successful retreatment can be achieved with other alloral , daa regimens , even when the retreatment regimen contains the same class of drug .
important considerations of this case report are the retreatment of a protease inhibitorexperienced patient with a second protease inhibitorcontaining regimen , the absence of rav testing prior to retreatment , and the timing of retreatment with respect to the persistence of ravs that emerged during initial treatment .
current european recommendations for the retreatment of patients who have failed a regimen containing one or more secondwave daas are based on indirect evidence ( hcv genotype , resistance profiles , the number of drugs administered , use of rbv , and treatment duration ) and state  intuitively , patients who failed on a daacontaining regimen should be retreated with an ifnfree combination including a drug with a high barrier to resistance ( currently , sofosbuvir ) , plus one or two other drugs , ideally with no crossresistance with the drugs already administered . based on results in difficulttocure patient populations , retreatment should be for 12 weeks with ribavirin , or extended to 24 weeks with or without ribavirin ( no data available comparing these approaches )  4 .
treatment guidelines from the american association for the study of liver disease suggest that ns5a and ns3 rav screening should be conducted prior to retreatment . it is recommended that patients without ns5a ravs should receive retreatment with ledipasvir / sofosbuvir with rbv for 24 weeks , those with ns5a ravs but without ns3 ravs receive simeprevir / sofosbuvir with rbv for 24 weeks , while sofosbuvir combined with either elbasvir / grazoprevir or paritaprevir / ritonavir / ombitasvir / dasabuvir may be efficacious in patients with ns5a and ns3 ravs ( data are limited ) 5 .
these recommendations are based , in part , on the observations that ns5a ravs are known to persist in the viral population for > 1 year , whereas ns3 ravs are less stable and have been shown to be gradually replaced with pretreatment ns3 sequence over time 6 .
although guidelines from both the eu and usa generally do not recommend retreating protease inhibitorexperienced patients with a second protease inhibitorcontaining regimen , successful retreatment with such regimens has been reported .
examples include daclatasvir / asunaprevir for the retreatment of ifn / rbv / telaprevirexperienced patients ( svr , 95.5% ) 7 , grazoprevir / elbasvir / rbv for the retreatment of ifn / rbv plus either telaprevir , boceprevir , or simeprevirexperienced patients ( svr , 96.2% [ 91.2% in patients with baseline ns3 ravs and 66.7% in patients with both ns3 and ns5a ravs at baseline ] ) 8 , and sofosbuvir / simeprevir with or without rbv for the retreatment of patients with experience of either telaprevir , boceprevir , paritaprevir , or gs9451 ( svr 93% ) 9 . in the study of sofosbuvir / simeprevir with ( n = 10 ) or without ( n = 5 ) rbv for the treatment of protease inhibitorexperienced patients , an overall svr rate of 93% ( n = 14/15 ) was achieved after a 12week treatment duration in a patient population that was considered to have 
difficult to cure  characteristics for this regimen ( hcv genotype 1a , high baseline viral levels , and prior nonresponse to protease inhibitors ) .
the single patient who did not achieve svr12 received sofosbuvir / simeprevir plus rbv and did not have ns3 ravs associated with resistance 9 months prior to treatment . of note ,
no patients had evidence of significant ns3 ravs ( three patients had ns3q80k , all of whom , including one recipient of sofosbuvir / simeprevir without rbv , achieved svr12 ) and the majority of patients received prior protease inhibitorbased therapy > 1 year prior to retreatment 9 .
this study and the current case report demonstrate that high rates of retreatment svr can be achieved without the use of rbv or extending retreatment duration to 24 weeks .
the addition of rbv and extension of treatment duration to 24 weeks is recommended in treatment guidelines as mechanisms to increase response , and delay or prevent the emergence of ravs , particularly when low barrier daas ( e.g. , protease inhibitors ) are used 4 , 5 .
the studies described above show that retreatment of proteaseexperienced patients with a second protease inhibitorcontaining regimen can be successful in carefully considered cases , despite no clear guideline support for this approach .
central factors in the success of this approach are the absence of significant crossresistance between the two regimens , and the timing of retreatment with respect to rav fitness and survivability .
as previously noted , plasma samples prior to retreatment for rav screening were not available , and retreatment with sofosbuvir plus simeprevir occurred 7 months after the initial treatment failure with daclatasvir plus asunaprevir .
this delay in retreatment may have allowed ns3 ravs to be replaced with pretreatment ns3 sequence over time 6 ; thus enabling a successful virologic outcome with a regimen containing the same hcv inhibitor class as asunaprevir ( such as simeprevir ) . in hcv
genotype 1b replicon in vitro assays , the presence of the ns3 d168v rav , which was detected at treatment failure , results in a 280fold loss of asunaprevir activity ( ec50 , 241 nm ) 10 and 2591fold loss of simeprevir activity ( ec50 , 17,917 nm ) 11 , compared with wildtype hcv genotype 1b replicons ; when tested in parallel using the same assay , the ec50 of asunaprevir and simeprevir in the hcv genotype 1b ns3d168v replicon were 200 nm and 5900 nm , respectively ( unpublished data ) .
the successful retreatment of this case study suggests that if ns3 ravs were present at the initiation of retreatment , the efficacy of sofosbuvir was sufficient to compensate for reduced simeprevir activity . in summary
, this case study demonstrates that hcv genotype 1binfected patients experiencing virologic failure with daclatasvir plus asunaprevir therapy have potential retreatment options , including regimens containing a component with a shared mechanism of action as the initial treatment .
r. safadi is an academic member at the hadassah medical organization and served as an advisory consultant of bristolmyers squibb .
 key clinical messagethere is currently minimal clinical experience regarding retreatment options for patients failing directacting antiviral combination regimens . here 
 , we report the outcomes of a hcv genotype 1binfected patient with virologic failure following treatment with daclatasvir and asunaprevir , who was successfully retreated with sofosbuvir plus simeprevir . 