Liquid chromatographic–mass spectrometric determination of the metabolism and disposition of the anti-retroviral nucleoside analogs zidovudine and lamivudine in C57BL/6N and B6C3F1 mice

Transmission of HIV from mother to infant can be effectively prevented by zidovudine (3′-azido-3′-deoxythymidine; AZT) alone or in combination with other anti-retroviral drugs; however, significant evidence for genotoxicity, including transplacental carcinogenicity in mice, has been reported for AZT. A method, based upon solid phase extraction (SPE) in the 96-well format, gradient liquid chromatography (LC), and electrospray mass spectrometry (MS), was developed and validated to measure serum concentrations in maternal C57BL/6N and fetal B6C3F1 mice of the nucleoside analogs AZT, lamivudine ((-)2′,3′-dideoxy-3′-thiacytidine; 3TC), and several metabolites selected based on importance in detoxification and bioactivation reactions. After intravenous (IV) and oral dosing with either 400 mg/kg AZT or 200 mg/kg 3TC, pharmacokinetics were determined for AZT, AZT-5′-glucuronide, 3′-amino-3′-deoxythymidine (AMT), AZT-5′-phosphate, 3TC, and 3TC-5′-phosphate in serum of adult female mice. Pharmacokinetics were also determined in spleen for AZT-5′-phosphate and 3TC-5′-phosphate following IV dosing. In addition, a preliminary assessment was made of placental transfer of AZT and 3TC and the presence of metabolites in the fetal compartment. The method described provides a means to evaluate thoroughly metabolism and disposition of anti-retroviral nucleoside analogs in maternal and fetal mice for comprehensive studies of genotoxicity.