Atazanavir is the first once-daily protease inhibitor for the treatment of human immunodeficiency virus type 1 infection and should be used only in combination therapy, as part of a highly active antiretroviral therapy (HAART) regimen. In addition to being the most potent protease inhibitor in vitro, atazanavir has a distinct cross-resistance profile that does not confer resistance to other protease inhibitors. However, resistance to other protease inhibitors often confers clinically relevant resistance to atazanavir.

Lopinavir (ABT-378) is an antiretroviral of the protease inhibitor class. It is used against HIV infections as a fixed-dose combination with another protease inhibitor, ritonavir, under the trade names Kaletra.

Ritonavir is a protease inhibitor with activity against Human Immunodeficiency Virus Type 1 (HIV-1). Ritonavir binds to the protease active site and inhibits the activity of the enzyme. It is FDA approved for the treatment of HIV-1 infection. In patients receiving medications metabolized by CYP3A or initiation of medications metabolized by CYP3A in patients already receiving Ritonavir, may increase plasma concentrations of medications metabolized by CYP3A. The most frequently reported adverse drug reactions among patients receiving Ritonavir alone or in combination with other antiretroviral drugs were gastrointestinal (including diarrhea, nausea, vomiting, abdominal pain (upper and lower)), neurological disturbances (including paresthesia and oral paresthesia), rash, and fatigue/asthenia.

Ombitasvir (ABT-267) is an antiviral drug for the treatment of hepatitis C virus (HCV) infection. Ombitasvir is a potent inhibitor of the hepatitis C virus protein NS5A, has favorable pharmacokinetic characteristics and is active in the picomolar range against genotype 1 - 6. In 2015, it was approved by FDA for use in combination with paritaprevir, ritonavir and dasabuvir in the product Viekira Pak for the treatment of HCV genotype 1.

Dasabuvir is a non-nucleoside inhibitor of the hepatitis C virus (HCV) NS5B palm polymerase inhibitor. It is used in the treatment of adult patients with chronic hepatitis C virus infection in combination with ombitasvir, paritaprevir, and ritonavir as the combination product Viekira Pak. Viekira PAK combines three direct-acting antiviral agents with distinct mechanisms of action and non-overlapping resistance profiles to target HCV at multiple steps in the viral lifecycle. Dasabuvir is extensively evaluated in large clinical trials and shown excellent sustained virological response among hepatitis C virus genotype1 patient population in combination with other oral direct acting antivirals, with good safety profile and tolerance.

Paritaprevir is a potent inhibitor of the NS3/4A protease that rapidly and consistently suppresses HCV. Paritaprevir is metabolized by the Cytochrome P450 isoform 3A (CYP3A); therefore, ritonavir was used concurrently to increase plasma concentrations and to prolong the half-life of this agent allowing for once-daily dosing. Several antiviral regimens combining paritaprevir with other agents have shown impressive results, tolerable side effects, and importantly, provided support of ‘all-oral’ interferon-free regimens against HCV. Paritaprevir monotherapy is discontinued now but paritaprevir is used as a component of Viekira Pak and Technivie for the treatment of patients with genotype 1 chronic hepatitis C virus (HCV) infection.