Anti-HIV activity of adefovir (PMEA) and PMPA in combination with antiretroviral compounds: in vitro analyses.

Adefovir (PMEA, 9-(2-phosphonomethoxyethyl)adenine), an acyclic nucleoside phosphonate analogue is active against retroviruses, hepadnaviruses and herpesviruses. Adefovir dipivoxil, an orally bioavailable prodrug of adefovir is currently in phase III clinical trials for the treatment of HIV and phase II clinical trials for the treatment of HBV infections. PMPA (9-(2-phosphonomethoxypropyl)adenine) is a related acyclic nucleoside phosphonate analogue that has demonstrated potent anti-SIV activity in rhesus macaques and recently has shown marked anti-HIV activity in a phase I clinical study. Since the standard of care for AIDS patients has become combination therapy, the effects of other antiretroviral compounds (d4T, ddC, AZT, ddI, 3TC, nelfinavir, ritonavir, indinavir, and saquinavir) on the anti-HIV activity of adefovir and PMPA were investigated in vitro. Adefovir and PMPA both demonstrated strong synergistic anti-HIV activity in combination with AZT. Adefovir demonstrated minor to moderate synergistic inhibition of HIV replication in combination with PMPA, d4T, ddC, nelfinavir, ritonavir, and saquinavir. PMPA demonstrated minor synergistic inhibition of HIV replication in combination with ddI and nelfinavir (and adefovir). All other combinations showed additive inhibition of HIV replication in vitro. Importantly, no antagonistic interactions were measured for any of the adefovir or PMPA combinations.