Specific routine determination of 3'-azido-3'-deoxythymidine (AZT) in plasma by partly automated liquid chromatography.

A simple isocratic HPLC method for determining azidothymidine (AZT) in serum and plasma of patients has been developed. The novel, specific, two-step, solid-phase extraction approach used for sample preparation gives a nearly quantitative recovery (95.3%) of AZT from the blood plasma matrix and requires only minimal handling of infectious clinical samples. Automatic "on-line" injection is achieved with an AASP system by switching a small cartridge, which retains the extracted analyte, into the HPLC stream. The overall HPLC procedure shows satisfying reproducibility with low standard deviation (CV: 2.1%). Because of the low detection limit (about 10 ng) and the possibility of concentrating AZT quantitatively in as much as 5 mL of plasma or serum, the method can be used in routine monitoring of AZT as well as in pharmacokinetic studies. Nevertheless, before establishing therapeutic drug monitoring for AZT, it still must be determined at what time after the last AZT dose blood specimens should be drawn for correct therapeutic interpretation of the concentration of AZT measured in blood.