HPLC-monitoring of AZT in HIV-infected patient's plasma: a critical study

3'-azido-2', 3'-deoxythymidine (AZT) concentrations in spiked human plasma were determined by means of reversed-phase high performance liquid chromatography (RP-HPLC). Samples were first cleaned-up for analysis using solid-phase extraction (SPE) columns filled with Silipore C18. In the concentration range comprising usual peak plasma concentrations during AZT therapy (0.1-20 mumol/l, i.e. 0.026-5.34 micrograms/ml) mean efficiency of the extraction procedure reached as high as 75.3% of original AZT concentrations in standard unextracted aqueous solutions. Replicate analyses in this range gave satisfactory intra-assay precision and reproducibility with coefficient of variation less than 11.3%. Calibration curves both in water and plasma showed good linearity (r > 0.999). The detection limit in plasma was 2 mumol/l, i.e. 5.3 ng per a 20 microliter of sample injected to the HPLC column. Plasma levels of AZT after a single dose administration, determined by HPLC and RIA showed rather poor correlation (r = 0.8900). In RIA about 1.7-4.5 times higher concentration values were obtained in a relatively short time, and, consequently, this method may better fulfil the needs of routine drug monitoring.