Clinical Pharmacokinetics of Paritaprevir

Paritaprevir is a potent hepatitis C virus (HCV) nonstructural (NS) protein 3/4A protease inhibitor that is used in combination with other direct-acting antivirals (DAAs) for the treatment of chronic HCV infection. Paritaprevir is primarily metabolized by cytochrome P450 (CYP) 3A4 and is administered with a low dose of ritonavir to achieve drug concentrations suitable for once-daily dosing. Coadministration of paritaprevir with ritonavir increases the half-life of single-dose paritaprevir from approximately 3 h to 5-8 h, doubles the time to maximum plasma concentration (T _max) from 2.3 to 4.7 h, and increases exposures 30-fold for maximum observed plasma concentration (C _max), 50-fold for area under the plasma concentration-time curve (AUC), and >300-fold for trough concentration (C ₂₄). Paritaprevir displays highly variable, nonlinear pharmacokinetics, with C _max and AUC increasing in a greater than dose proportional manner when administered with or without ritonavir. In the presence of ritonavir, paritaprevir is excreted mostly unchanged in feces via biliary excretion. Paritaprevir exposures are higher in Japanese subjects compared with Caucasian subjects; however, no dose adjustment is needed for Japanese patients as the higher exposures are safe and well tolerated. The pharmacokinetic characteristics of paritaprevir are similar between healthy subjects and HCV-infected patients, and are not appreciably altered by mild or moderate hepatic impairment or mild, moderate, or severe renal impairment, including those on dialysis. Paritaprevir exposures are increased in patients with severe hepatic impairment. Although the presence of a low dose of ritonavir in paritaprevir-containing regimens increases the likelihood of drug-drug interactions, results from several drug interaction studies demonstrated that paritaprevir-containing regimens can be coadministered with many comedications that are commonly prescribed in HCV-infected patients.