Interactions among combinations of two and three protease inhibitors against drug-susceptible and drug-resistant HIV-1 isolates

Protease inhibitors used in combination with reverse transcriptase inhibito rs have demonstrated potent anti-HIV-1 activity in vitro as well as in vivo . We evaluated interactions among five protease inhibitors: indinavir (IDV) , ritonavir (RTV), saquinavir (SQV), amprenavir (APV), and nelfinavir (NFV) , when used in combinations of two and three drugs in vitro against several HIV-1 isolates, including those susceptible and resistant to various nucle oside and nonnucleoside reverse transcriptase inhibitors. Interactions rang ed from synergy to slight antagonism depending on the viral isolates and th e experimental conditions employed. Further clinical evaluation of protease inhibitor combinations is warranted.