A Drug-drug Interaction Study Between Daclatasvir and Atazanavir/Ritonavir or Atazanavir/Cobicistat

Approximately 20-25% of the total number of HIV-infected patients is co-infected with HCV which translates to 6-8 million persons worldwide. Combined treatment of HIV and HCV is complicated by the risk of drug-drug interactions as both the direct acting antiviral agents (DAAs) for HCV as the antiretroviral agents for HIV are substrates of cytochrome P450 (CYP450) or various membrane transporters, and also have the capacity to influence these systems. A careful selection of the appropriate regimens and if needed adjusted doses is key for optimal treatment of both viral infections. Daclatasvir is a recently approved anti-HCV agent that is a CYP3A4 substrate but does not affect CYP450 itself. It is also a moderate inhibitor of various membrane transporters such as organic anion-transporting polypeptide (OATP1B1), P-glycoprotein (P-gP), and organic cation transporters (OCT2). Atazanavir/ritonavir is one of the preferred antiretroviral agents in all international guidelines. Ritonavir is used as a boosting agents based on its inhibitory effects on CYP3A. This also inhibits CYP3A-mediated metabolism of daclatasvir and when atazanavir/ritonavir is combined with daclatasvir, it is recommended to reduce the dose of daclatasvir from 60mg QD to 30mg QD. Cobicistat has recently been approved as an alternative booster of atazanavir at a dose of 150mg QD. It is expected that cobicistat will inhibit CYP3A mediated metabolism of daclatasvir in a similar manner as ritonavir does, but there are no clinical data to support this. As cobicistat lacks some of the adverse events associated with ritonavir use, the use of cobicistat, including as a booster of atazanavir, is likely to increase. This study aims to provide the evidence that 150mg of cobicistat will have the same effect on the pharmacokinetics of daclatasvir 30mg QD as 100mg of ritonavir, when given together with atazanavir 300mg.