Rapid and simultaneous determination of zidovudine and its glucuronide metabolite in plasma and urine. Application to the pharmacokinetic interaction of zidovudine and probenecid in the monkey

Abstract

Quantitation of zidovudine (3’-azido-3’-deoxythymidine, AZT) in biological medium is required for determination of its pharmacokinetics, and as a means to evaluate clinical dosage regimens. Analytical methods have been reported to measure AZT, and in some cases its 5’-O-glucuronide (AZTG) metabolite in plasma or serum and urine samples of man and experimental animals [l-8]. Most of these procedures are able to quantitate AZT in serum utilizing liquid chromatography (LC) [l-7]. These techniques are suitable when therapeutic drug monitoring or pharmacokinetic analyses of AZT are desired. Characterization of the metabolism of AZT also requires quantitation of AZTG in plasma and urine. Information on the combined disposition of AZT and AZTG is critical to the evaluation and interpretation of the pharmacokinetic basis of drug interactions with AZT. Of the methods reported, Good et al. [l] and Lacroix et al. [7] have developed procedures to quantitate AZT and AZTG simultaneously in human serum. The latter method [7] has also been applied to AZT and AZTG in urine. The method of Good et al. [l] cannot be used for the analysis of AZT and AZTG in urine because of interferences from endogeneous substances. Measurement of AZT and AZTG in urine according to Blum et al. [5], required gradient elution with analysis times of 30 min. Simultaneous measurement of AZT and AZTG in human serum or urine by the method of Lacroix et al. [7] required column switching. The monkey has been shown to exhibit pharmacokinetics of AZT most similar to man [8], and should serve as an appropriate animal model to characterize drug interactions of AZT. Because AIDS patients are exposed to multiple and variable drug combinations, monkeys permit controlled and comprehensive, intravenous and oral dosing, pharmacokinetic investigations to be conducted. The purpose of this investigation was to develop an LC method to quantitate AZT and AZTG simultaneously in monkey plasma and urine. The method would have to utilize a small plasma volume, and provide a level of quantitation necessary to investigate the pharmacokinetic basis of drug interactions with AZT.