The active metabolites in humans: 67M-1, 67M-2 and 67M-4 (top to bottom)
Febuxostat has three active metabolites in humans, which are formed mainly by a number of cytochrome P450 liver enzymes (CYP1A1, 1A2, 2C8, 2C9). One of them is a dicarboxylic acid, the other two are hydroxylated derivatives. These, as well as the original drug, are further glucuronidated, mainly by the enzymes UGT1A1, 1A8, and 1A9. Febuxostat and its metabolites are eliminated via the urine (49% of the total substance, comprising 3% unchanged febuxostat, 30% febuxostat glucuronide, 13% active metabolites and their glucuronides, and 3% unknown entities) and via the faeces (45%, of which 12% unchanged febuxostat, 1% glucuronide, 25% active metabolites and their glucuronides, and 7% unknown entities). Elimination half-life is five to eight hours.
