Single daily doses of saquinavir achieve HIV-inhibitory concentrations when combined with baby-dose ritonavir.

Dual protease inhibitor (PI) therapy has been established either in order to increase plasma concentrations of one PI or to combine synergistic effects of two PI's on viral load. Studies with saquinavir (SQV) and small doses of ritonavir (RTV) as well as experiences from our therapeutic drug monitoring suggest that single daily doses may result in sufficient SQV serum levels throughout an interval of 24 h. A controlled, randomized trial with 20 healthy men was conducted for the comparison of serum levels with 1600 mg SQV (group 1) or 1600 mg SQV/200 mg RTV (group 2). The dosages were selected in order to use RTV as an inhibitor of cytochrome P450 3A4 and SQV as protease inhibitor. The volunteers received single daily doses following a standardized breakfast on 3 consecutive days. Serum samples were analyzed for SQV and RTV employing LC-tandem mass spectrometry. The minimum concentration of saquinavir after 24 hours, the AUC, the maximum concentration and the serum half-lives on day 3 served as target parameters. The minimum SQV concentration amounted to 469.4 ng/ml, when combined with RTV and proved to be significantly higher (p <0.05) than the corresponding concentration with SQV alone (127.3 ng/ml). The SQV maximum concentration was raised approximately 6fold and the AUC 9fold when RTV was coadministered. In combination with 200 mg of RTV the predominant elimination half-life of SQV increased from 2.6 to 6.45 hours. These data prove that under single daily doses of 1600 mg SQV/200 mg RTV HIV-inhibitory concentrations of SQV can be achieved for 24 hours. Due to the high variability of the concentrations, which can be seen with all PI s, we recommend continuous therapeutic drug monitoring of serum trough levels.