HIV-1 is a chronic infection for which there is currently no cure—the prospect of maintaining therapy for the lifetime of a patient presents major challenges. The potential for persistent viral replication in compartments and reservoirs may continue to drive pathogenic disease processes (Finzi et al. 1997, 1999). The effect of therapy can be impaired by nonadherence, poor drug tolerability, and drug interactions among antiretroviral agents and other medications that decrease optimal drug levels. Each of these can lead to virologic failure and the evolution of drug resistance.