Determination of indinavir in plasma by solid-phase extraction and column liquid chromatography

Indinavir is a specific and potent HIV protease inhibitor. A new column liq uid chromatographic method for the determination of this drug is described. This assay was developed for the clinical monitoring of trough concentrati ons in AIDS patients, using a I-mt plasma sample volume. Determination of i ndinavir was made by a rapid solid-phase extraction procedure with the new polymeric Oasis HLB sorbent followed by a reversed-phase liquid chromatogra phy and a UV detection at 210 nm. A weighted least squares linear regressio n (weighting factor = 1/y where y = peak height ratio) was used to calculat e the equation relating the peak-height ratio of the drug and the internal standard to the concentration of indinavir in the range 10-800 ng/mL (0.014 -1.124 mu M). At the lower limit of quantification (10 ng/mL), the mean acc uracy was 102 +/-7% and 104 +/- 11% for within- and between-day analysis, r espectively. The limit of detection, based on a signal-to-noise ratio of 2: 1, was 4 ng/mL (0.006 mu M). Compounds of interest were eluted from the ext raction cartridges with 300 mu L of mobile phase, and mean absolute recover ies of indinavir and internal standard were 66.4% and 80.3%, respectively. No metabolite of indinavir was found to co-elute with the drug or its inter nal standard. Among the tested drugs, especially nucleoside analogues and t he other protease inhibitors used in clinical care, none was found to inter fere with the assay at this time. This simple and selective method is suita ble for therapeutic indinavir monitoring.