RBV, a nucleoside analogue, is used for the treatment of hepatitis C virus (HCV) in alliance with interferon-alfa 2a/2b in patients with HIV-1. The mechanism of action of RBV has led to in vitro studies examining the agonism/antagonism in efficacy occurring when used in combination with nucleoside reverse transcriptase inhibitors (NRTIs). The primary objective of the pharmacology component of this current study will be the evaluation of the effect of RBV on the intracellular activation of ZDV or d4T owing to the reported antagonism observed in vitro.

Pharmacokinetic (PK) evaluations for plasma ZDV or d4T and intracellular ZDV or d4T and measurements of their triphosphate anabolites are performed before initial RBV dosing (within 2 weeks of visit) and 8 weeks after RBV administration. Thymidine triphosphate (TTP) concentrations also are quantitated to permit estimation of the ratio of active drug to endogenous triphosphate concentrations. For entry, prior to RBV dosing, blood samples are collected within 2 hours prior to the ZDV or d4T dose and then at Hours 1, 4, and 8 post dosing. Following the entry PK blood draws, patients initiate RBV treatment within 2 weeks of the first PK study day. For the Week 8 evaluation (measured as 8 weeks following initiation of RBV), blood samples are collected prior to the ZDV or d4T dose and then at Hours 1, 4, and 8 post dosing.