TY - JOUR T1 - Pharmacokinetics, Metabolism, and Excretion of [<sup>14</sup>C]Axitinib, a Vascular Endothelial Growth Factor Receptor Tyrosine Kinase Inhibitor, in Humans JF - Drug Metabolism and Disposition JO - Drug Metab Dispos SP - 918 LP - 931 DO - 10.1124/dmd.113.056531 VL - 42 IS - 5 AU - Bill J. Smith AU - Yazdi Pithavala AU - Hai-Zhi Bu AU - Ping Kang AU - Brian Hee AU - Alan J. Deese AU - William F. Pool AU - Karen J. Klamerus AU - Ellen Y. Wu AU - Deepak K. Dalvie Y1 - 2014/05/01 UR - http://dmd.aspetjournals.org/content/42/5/918.abstract N2 - The disposition of a single oral dose of 5 mg (100 μCi) of [14C]axitinib was investigated in fasted healthy human subjects (N = 8). Axitinib was rapidly absorbed, with a median plasma Tmax of 2.2 hours and a geometric mean Cmax and half-life of 29.2 ng/ml and 10.6 hours, respectively. The plasma total radioactivity-time profile was similar to that of axitinib but the AUC was greater, suggesting the presence of metabolites. The major metabolites in human plasma (0–12 hours), identified as axitinib N-glucuronide (M7) and axitinib sulfoxide (M12), were pharmacologically inactive, and with axitinib comprised 50.4%, 16.2%, and 22.5% of the radioactivity, respectively. In excreta, the majority of radioactivity was recovered in most subjects by 48 hours postdose. The median radioactivity excreted in urine, feces, and total recovery was 22.7%, 37.0%, and 59.7%, respectively. The recovery from feces was variable across subjects (range, 2.5%–60.2%). The metabolites identified in urine were M5 (carboxylic acid), M12 (sulfoxide), M7 (N-glucuronide), M9 (sulfoxide/N-oxide), and M8a (methylhydroxy glucuronide), accounting for 5.7%, 3.5%, 2.6%, 1.7%, and 1.3% of the dose, respectively. The drug-related products identified in feces were unchanged axitinib, M14/15 (mono-oxidation/sulfone), M12a (epoxide), and an unidentified metabolite, comprising 12%, 5.7%, 5.1%, and 5.0% of the dose, respectively. The proposed mechanism to form M5 involved a carbon-carbon bond cleavage via M12a, followed by rearrangement to a ketone intermediate and subsequent Baeyer-Villiger rearrangement, possibly through a peroxide intermediate. In summary, the study characterized axitinib metabolites in circulation and primary elimination pathways of the drug, which were mainly oxidative in nature. ER -