Role of ritonavir in the drug interactions between telaprevir and ritonavir-boosted atazanavir.

BACKGROUND Detrimental bidirectional pharmacokinetic interactions have been observed when telaprevir (TVR) and ritonavir (RTV)-boosted human immunodeficiency virus (HIV) protease inhibitors are coadministered in healthy volunteers. Our aim was to evaluate the role of RTV in the bidirectional TVR and atazanavir (ATV) interactions. METHOD An open-label, sequential study was carried out in hepatitis C virus (HCV)/HIV-coinfected patients on a RTV-boosted ATV-based (ATVr) antiretroviral regimen (300/100 mg every 24 hours) and triple therapy for chronic C hepatitis genotype 1 (TVR, 1125 mg every 12 hours, pegylated interferon-alpha and ribavirin). Pharmacokinetic profiles were acquired before and after switching from ATVr to unboosted ATV (200 mg every 12 hours). The plasma levels of both drugs were determined by liquid chromatography coupled with mass spectrometry. Pharmacokinetic parameters were calculated by noncompartmental analysis and compared by geometric mean ratios and their 90% confidence intervals. RESULTS Fourteen white HCV/HIV-coinfected males were enrolled in this study. After RTV was withdrawn, the TVR AUC(0-12) (area under the concentration-time curve), maximum concentration (C(max)), and minimum concentration (C(min)) values increased by 19% (7%-30%), 12% (0.9%-29%), and 18% (2%-34%), respectively, without any changes in the TVR terminal half-life. The ATV AUC(0-12), C(max), and C(min) values were 39% (13%-66%), 19% (8%-59%), and 48% (1%-96%) higher, respectively, with a significantly shorter terminal half-life (22.6 hours vs 10.4 hours). CONCLUSIONS RTV is responsible for the adverse interactions that occur when TVR and ATVr are administered together, possibly by influencing either the absorption phase or first-pass metabolism of TVR. The boost effect of TVR on ATV exposure is higher than on RTV, despite its shorter terminal half-life. The coadministration of TVR and unboosted ATV results in increased exposure of both drugs compared with their coadministration with RTV. CLINICAL TRIALS REGISTRATION ClinicalTrials.gov: NCT01818856. European Medicines Agency EudraCT no. 2012-002515-25.