Biol. Pharm. Bull. 30(10) 1947—1949 (2007)

treat human immunodeficiency virus (HIV) type-1. According to in vitro experiments, DRV was active against HIV-1 with PI resistance mutations and against PI resistant clinical isolates. This drug is expected to be effective in antiretroviral treatment-experienced patients, such as those possessing HIV-1 strains which are resistant to more than one PI. Bouche et al. recently determined plasma DRV concentrations using liquid chromatography-tandem mass spectrometry (LC/MS/MS). However, as LC/MS/MS equipment is very expensive and unavailable in conventional hospital laboratories, development of alternate methods is necessary. We have already developed a simple HPLC method for simultaneous quantitative determination of seven HIV protease inhibitors and efavirenz. We expect DRV can be measured using this method because amprenavir, whose chemical structure is quite similar to DRV, was successfully measured. In this study we aimed to validate the measurement of plasma DRV concentrations using the HPLC method. This is the first report where plasma DRV concentration has been measured using this HPLC method.