Raltegravir is predominantly metabolised by hepatic glucuronidation via the uridine diphosphate glucuronosyltransferase 1A1 (UGT1A1) isozyme. A small component is renally excreted (~9%). In three double-blind, randomised studies of pharmacokinetics, safety and tolerability, raltegravir was found to be rapidly absorbed with a terminal half-life of 7-12 hours. It exhibited potent in vitro inhibition with a 95% inhibitory concentration (IC95) = 33nM in 50% human serum. Pharmacokinetic analyses of various dosing regimens supported the use of twice daily dosing of multiple doses of 100mg and greater. Results from a study investigating once daily dosing are pending.