 When in the bloodstream, 99.2% of the substance is bound to the plasma protein albumin, and 82–91% of the active metabolites are bound to plasma proteins.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.