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.
UGT2B7 is one of the most important hepatic UGTs for drug glucuronidation; numerous drug substrates have been shown to be glucuronidated by UGT2B7 (e.g. opioids, nonsteroidal anti-inflammatory drugs (NSAIDs), steroids, antivirals). UGT2B7 is abundant in both liver and intestine. Selective substrates include morphine, codeine and zidovudine (AZT).