UDP-glucuronosyltransferases (UGT) represent the major phase II drug metabolism pathway in human. UGT enzymes catalyze the transfer of glucuronic acid (derived from UDPGA co-factor) to xenobiotics and endogenous substrates having nucleophilic acceptor groups, making them more polar and readily excreted in urine or bile. To date, at least 18 human UGT enzymes have been cloned and sequenced. Like the P450 enzymes, UGTs possess broad and overlapping substrate specificities. Clinically relevant drug interactions have been identified for UGT isoforms, leading regulatory agencies (FDA) to require drug interaction testing for compounds showing significant UGT metabolism.
UGT2B15 expressed in the liver as well as intestine. This enzyme is involved in the inactivation of steroid hormones, mainly androgens. Evidence also suggest UGT2B15 is able to metabolize several classes of xenobiotic substrates, including simple phenolic compounds, 7-hydroxylated coumarins, flavonoids, anthraquinones and other drugs and their hydroxylated metabolites. S-oxazepam and S-lorazepam are selective for UGT2B15.