Antiretroviral Drug Interaction Study in Volunteers With HIV

The incidence of opportunistic infections such as Pneumocystis jirovecii pneumonia (PCP) and Toxoplasma gondii have substantially declined in patients with HIV infection due to potent combination antiretroviral (ARV) therapy and effective prophylaxis. The drug of choice for prophylaxis and treatment of PCP and toxoplasmosis is trimethoprim-sulfamethoxazole (TMP-SMX) and sulfadiazine, respectively. In patients who cannot tolerate these first line therapies, atovaquone is a common alternative. While generally considered safe and effective, a recent drug interaction study involving a single dose of combination tablet of atovaquone/proguanil (Malarone ) in HIV-infected patients showed that atovaquone plasma concentrations were significantly lowered (compared to healthy volunteers) by 75%, 74%, and 46% in patients taking the ARV medications efavirenz (EFV), lopinavir-ritonavir (LPV/r), and atazanavir-ritonavir (ATV/r), respectively. The mechanism of this drug interaction is unknown but is presumably due to induction of uridine diphosphate glucuronsosyltransferase (UGT) enzymes responsible for the metabolism of atovaquone. The magnitude of this interaction is such that it strongly suggests a clinically relevant drug interaction between atovaquone and the aforementioned ARVs. The purpose of this study is to determine whether HIV-infected subjects receiving ATV/r or EFV-containing ARV regimens, experience reductions in atovaquone exposure under steady state conditions compared to HIV-infected patients not receiving ARV therapy. In this open-label study, 30 HIV-infected subjects will participate in 1 of 3 groups of 10 (Groups A, B, and C). Group A will consist of 10 subjects who are already receiving combination ARV therapy containing ATV/r; Group B will consist of 10 subjects already receiving combination ARV therapy containing EFV; and Group C will consist of 10 subjects who are not currently receiving ARV therapy. All subjects in Groups A, B, and C will be randomly assigned to either receive atovaquone 750 mg twice daily for 14 days (Phase 1) followed by a 2-6 week washout period, followed by atovaquone 1500 mg twice daily for 14 days (Phase 2), or vice versa. Pharmacokinetic (PK) sampling for atovaquone will occur on Day 14 of Phase 1 and 2. Atovaquone PK parameters will be determined using non-compartmental methods with the WinNonlin professional computer program (version 5.2; Pharsight Corporation, Mountain View, CA). The following PK parameters will be compared among the groups: area under the concentration vs. time curve (AUC ?), maximum concentration (Cmax), apparent oral clearance (Cl/F), time to reach maximum concentration (Tmax), and half-life (T (Omega)). Data from this investigation will determine whether ATV/r and/or EFV alter the steady state PK of atovaquone in HIV-infected subjects. This information will assist clinicians in choosing appropriate alternative therapies for the treatment of PCP and toxoplasmosis in patients who are not candidates for first line therapies.