Identification and profiling of circulating metabolites of atazanavir, a HIV protease inhibitor

Atazanavir is a commonly prescribed protease inhibitor for treatment of HIV-1 infection. Thus far, only limited data are available on the in vivo metabolism of the drug. Three systemic circulating metabolites have been reported, but their chemical structures have not been released publicly. Atazanavir metabolites may contribute to its effectiveness but also to its toxicity and interactions. Thus, there is a need for extensive metabolic profiling of atazanavir. Our goals were to screen and identify previously unknown atazanavir metabolites and to develop a sensitive metabolite profiling method in plasma. Five atazanavir metabolites were detected and identified in patient samples using liquid chromatography coupled to linear ion trap mass spectrometry: one N-dealkylation product (M1), two metabolites resulting from carbamate hydrolysis (M2 and M3), a hydroxylated product (M4), and a keto-metabolite (M5). For sensitive semiquantitative analysis of the metabolites in plasma, the method was transferred to liquid chromatography coupled to triple quadrupole mass spectrometry. In 12 patient samples, all the metabolites could be detected, and possible other potential atazanavir keto-metabolites were found. Atazanavir metabolite levels were positively correlated with atazanavir levels, but interindividual variability was high. The developed atazanavir metabolic screening method can now be used for further clinical pharmacological research with this antiretroviral agent.