Azole antifungal agents (azoles) have inhibitory effects on the cytochrome P450. However, the effect of azoles on conjugative metabolism has not been given much attention. Lorazepam (LZP), a benzodiazepine sedative agent, is known to be metabolized by uridine 5'-diphosphate (UDP)-glucuronyltransferase. Herein we report investigation of the effect of azoles on the enzyme-kinetics of glucuronidation of lorazepam using rabbit liver microsomes in vitro. The Km and Vmax for LZP glucuronidation were determined to be 0.26+/-0.08 mM and 1.25+/-0.21 nmol/min/mg protein, respectively, when evaluated in the presence of a detergent 3-[(3-cholamidopropyl)-dimethylammonio]-1-propanesulfonate (CHAPS) (0.8 mg/mg protein). Azoles fluconazole, miconazole, and ketoconazole competitively inhibited the glucuronidation of LZP, with Ki values of 7.17+/-4.78 mM, 0.17+/-0.08 mM, and 0.092+/-0.026 mM, respectively. These results are comparable to the previously reported Ki values of azoles with zidovudine (AZT) glucuronidation (1.4, 0.18, and 0.08 mM for fluconazole, miconazole, and ketoconazole, respectively) [Sampol et al., Br. J. Clin. Pharmacol., 40, 83-86, 1995]. Therefore, in order to avoid possible side effects of LZP, the concomitant administration of LZP and azoles should be carefully evaluated.