Excretion and Metabolism of Lersivirine (5-{[ 3,5-Diethyl-1-(2-hydroxyethyl)(3,5-14C2)-1H-pyrazol-4-yl]oxy}benzene-1,3-dicarbonitrile), a Next- Generation Non-Nucleoside Reverse Transcriptase Inhibitor, after Administration of [14C]Lersivirine to Healthy Volunteers

Lersivirine [UK-453,061, 5-((3,5-diethyl-1-(2-hydroxyethyl)(3,5-C-14(2))- 1H-pyrazol-4-yl) oxy) benzene-1,3-dicarbonitrile] is a nextgeneration non-nucleoside reverse transcriptase inhibitor, with a unique binding interaction within the reverse transcriptase binding pocket. Lersivirine has shown antiviral activity and is well tolerated in HIV-infected and healthy subjects. This open-label, Phase I study investigated the absorption, metabolism, and excretion of a single oral 500-mg dose of [C-14] lersivirine (parent drug) and characterized the plasma, fecal, and urinary radioactivity of lersivirine and its metabolites in four healthy male volunteers. Plasma C-max for total radioactivity and unchanged lersivirine typically occurred between 0.5 and 3 h postdose. The majority of radioactivity was excreted in urine (similar to 80%) with the remainder excreted in the feces (similar to 20%). The blood/ plasma ratio of total drug-derived radioactivity [area under the plasma concentration-time profile from time zero extrapolated to infinite time (AUC(int))] was 0.48, indicating that radioactive material was distributed predominantly into plasma. Lersivirine was extensively metabolized, primarily by UDP glucuronosyltransferaseand cytochrome P450-dependent pathways, with 22 metabolites being identified in this study. Analysis of precipitated plasma revealed that the lersivirine-glucuronide conjugate was the major circulating component (45% of total radioactivity), whereas unchanged lersivirine represented 13% of total plasma radioactivity. In vitro studies showed that UGT2B7 and CYP3A4 are responsible for the majority of lersivirine metabolism in humans.