Ritonavir inhibits the two main prasugrel bioactivation pathways in vitro: a potential drug–drug interaction in HIV patients Youssef Daali ⁎ , Virginie Ancrenaz, Marija Bosilkovska, Pierre Dayer, Jules Desmeules Division of Clinical Pharmacology and Toxicology, Geneva University Hospitals, Geneva, Switzerland ARTICLE INFO ABSTRACT Article history: Received 25 January 2011 Accepted 22 March 2011 Prasugrel is an antiplatelet prodrug used in patients with acute coronary syndrome. Prasugrel is mainly bioactivated by cytochromes P450 3A4/5 and CYP2B6. HIV patients are at risk of cardiovascular disease, and the protease inhibitor ritonavir is a potent inhibitor of these 2 CYPs. The aim of this in vitro study was to determine the impact of ritonavir in prasugrel metabolism. Human liver microsomes (HLMs) and recombinant microsomes were used to identify the enzymes responsible for the bioactivation of prasugrel. Prasugrel concentrations of 5 to 200 μM were used for Km determination. Inhibition by ritonavir was characterized using HLMs at concentrations of 0.1 to 30 μM. Prasugrel active metabolite determination was performed with a validated liquid chromatography-mass spectrometry method. Using recombinant microsomes, prasugrel biotransformation was mainly performed by CYP2B6, CYP2D6, CYP2C19, CYP3A4, and CYP3A5. With specific inhibitors of CYP3A, CYP2B6, CYP2D6, CYP2C9, and CYP2C19, active metabolite production was decreased by 38% ± 15% with 4-(4-chlorobenzyl)pyridine (CYP2B6 inhibitor) and by 45 ± 16% with ketoconazole (CYP3A inhibitor). The Km value for prasugrel metabolism in HLMs was determined to be 92.5 μM. Ritonavir at 0.1 to 30 μM was shown to be a potent dose- dependent inhibitor of prasugrel. In this in-vitro study, we found a potent inhibition of prasugrel bioactivation by ritonavir compared to the specific inhibitors of CYP3A and CYP2B6 due to the simultaneous inhibition of CYP2B6 and CYP3A by ritonavir. This finding suggests a potential significant drug–drug interaction between these two drugs. © 2011 Elsevier Inc. All rights reserved. 1. Introduction Cardiovascular diseases constitute more than 10% of deaths in human immunodeficiency virus (HIV)-infected patients [1], and recent studies have shown that cardiovascular diseases were one of the most common complications observed in HIV-infected patients [2,3]. An associative risk between HIV infection and coronary artery disease was suspected through an inflammatory process of atherosclerosis [4]. Moreover, metabolic side effects associated with antiretroviral therapy, including hypercholes- terolemia, hyperglyceridemia and lipodystorphy syndrome, enhance the risk of cardiovascular events in HIV population [5]. METABOLISM CLINICAL AND EXPERIMENTAL 60 (2011) 1584 – 1589 Funding: This work was supported by the APSI Department of Geneva University Hospitals. Disclosure statement: None of the authors declares any conflict of interest regarding this manuscript. Author contributions: Youssef Daali: -Research design -Analytical methods -Data analysis -Writing manuscript Virginie Ancrenaz: -Conducted experiments -Analytical methods -Data analysis -Writing manuscript Marija Bosilkovska: - Conducted experiments -Data analysis Pierre Dayer: -Research design -Writing manuscript Jules Desmeules: -Research design -Data analysis -Writing manuscript. ⁎ Corresponding author. Tel.: +41 (0)22 3795430; fax: +41 (0)22 3829945. E-mail address: youssef.daali@hcuge.ch (Y. Daali). 0026-0495/$ – see front matter © 2011 Elsevier Inc. All rights reserved. doi:10.1016/j.metabol.2011.03.015 Available at www.sciencedirect.com Metabolism www.metabolismjournal.com