Pharmacokinetics and resistance mutations affect virologic response to ritonavir/saquinavir-containing regimens

The authors assessed the impact of protease and reverse transcription (RT) mutations and individual pharmacokinetic parameters on virologic response to a four-drug regimen including ritonavir/saquinavir. Treatment was given at the start of the study (M0) to 22 HIV-1 protease inhibitor-naive or pretreated patients. Protease and RT genes were sequenced at M0, at the time of virologic failure, or at the end of the follow-up. Plasma ritonavir and saquinavir peak C(max), C(min), and area under the curve (AUC) were determined based on samples taken 0, 1, 2, 3, 4, 6, 8, and 12 hours after administration. HIV-1 RNA decreased to less than 50 copies/mL in 11 patients (group 1). At M0, five of them had no RT mutation and 10 had three or fewer secondary protease mutations with no new mutation during follow-up. Ritonavir and saquinavir pharmacokinetics showed wide interindividual variability. Treatment failed in 11 patients (group 2): 9 had three to eight protease mutations and a mean of 5.8 RT mutations at M0, with emergence of new mutations during follow-up. Pharmacokinetics was similar to those of group 1. The other two patients with virologic failure showed no baseline primary mutation but were the only patients with insufficient saquinavir and ritonavir AUC. The authors showed the complementarity between drug-resistance genotype and individual pharmacokinetics and the potential utility of AUC and Cmax to manage treatment.