Ritonavir
Ritonavir is an HIV protease inhibitor that interferes with the reproductive cycle of HIV. Although it was initially developed as an independent antiviral agent, it has been shown to possess advantageous properties in combination regimens with low-dose ritonavir and other protease inhibitors. It is now more commonly used as a booster of other protease inhibitors and is available in both liquid formulations and as capsules.   While ritonavir is not an active antiviral agent against hepatitis C virus (HCV) infection, it is added in combination therapies indicated for the treatment of HCV infections as a booster. Ritonavir is a potent CYP3A inhibitor that increases peak and trough plasma drug concentrations of other protease inhibitors such as [DB09297] and overall drug exposure. American Association for the Study of Liver Diseases (AASLD) and the Infectious Diseases Society of America (IDSA) guidelines recommend ritonavir-boosted combination therapies as first-line therapy for HCV Genotype 1a/b and 4 treatment-naïve patients with or without cirrhosis.   Ritonavir is found in a fixed-dose combination product with [DB09296], [DB09183], and [DB09297] as the FDA-approved product Viekira Pak. First approved in December 2014, Viekira Pak is indicated for the treatment of HCV genotype 1b without cirrhosis or with compensated cirrhosis, and when combined with Ribavirin for the treatment of HCV genotype 1a without cirrhosis or with compensated cirrhosis.  Ritonavir is also available as a fixed-dose combination product with [DB09296] and [DB09297] as the FDA- and Health Canada-approved product Technivie. First approved in July 2015, Technivie is indicated in combination with Ribavirin for the treatment of patients with genotype 4 chronic hepatitis C virus (HCV) infection without cirrhosis or with compensated cirrhosis.  In Canada, ritonavir is also available as a fixed-dose combination product with [DB09296], [DB09183], and [DB09297] as the Health Canada-approved, commercially available product Holkira Pak. First approved in January 2015, Holkira Pak is indicated for the treatment of HCV genotype 1b with or without cirrhosis, and when combined with Ribavirin for the treatment of HCV genotype 1a with or without cirrhosis. The inclusion of ritonavir can select for HIV-1 protease inhibitor resistance-associated substitutions. Any HCV/HIV-1 co-infected patients treated with ritonavir-containing combination therapies should also be on a suppressive antiretroviral drug regimen to reduce the risk of HIV-1 protease inhibitor drug resistance.  Ritonavir is used in combination with other drugs to treat coronavirus disease 2019 (COVID-19) in patients who are at risk for progressing into a severe form of the disease.