RT Journal Article
SR Electronic
T1 Stereoselective Glucuronidation of Ornidazole in Humans: Predominant Contribution of UDP-Glucuronosyltransferases 1A9 and 2B7
JF Drug Metabolism and Disposition
JO Drug Metab Dispos
FD American Society for Pharmacology and Experimental Therapeutics
SP 1306
OP 1318
DO 10.1124/dmd.113.051235
VO 41
IS 7
A1 Jiangbo Du
A1 Tiangeng You
A1 Xiaoyan Chen
A1 Dafang Zhong
YR 2013
UL http://dmd.aspetjournals.org/content/41/7/1306.abstract
AB Ornidazole [R,S-1-chloro-3-(2-methyl-5-nitro-1H-imidazol-1-yl)propan-2-ol] is a chiral 5-nitroimidazole class antimicrobial agent. This study aimed to investigate the principal metabolic pathway of ornidazole in humans and identify the major enzymes involved. A total of 19 metabolites were identified in human urine collected from patients with hepatobiliary diseases after an intravenous drip infusion of 500 mg of racemic ornidazole. Stereoselective glucuronidation, followed by renal excretion, was the principal metabolic pathway of ornidazole in humans, accounting for 37.3% of the administered dose. Screening assays with 12 available human recombinant UDP-glucuronosyltransferases (UGTs) demonstrated that UGT1A9 was the predominant UGT isoform involved in R-ornidazole glucuronidation, whereas S-ornidazole glucuronidation was almost exclusively catalyzed by UGT2B7. Chemical inhibition study with niflumic acid and flurbiprofen supported these findings. Enzyme kinetic parameters were then determined in human liver microsomes (HLMs), human kidney microsomes (HKMs), UGT1A9, and 2B7. The Km values for UGT1A9 (15.6 ± 1.6 mM for R-ornidazole) and 2B7 (3.8 ± 0.9 mM for S-ornidazole) were quite similar to those determined in HLMs and HKMs (20.1 ± 1.4 and 17.7 ± 4.0 mM for R-ornidazole; 6.6 ± 1.3 and 3.2 ± 0.4 mM for S-ornidazole). The in vitro intrinsic clearance (CLint) ratios of S- to R-ornidazole were approximately 4.3 in HLMs and 6.5 in HKMs, respectively. The hepatic and renal clearances were estimated based on the well-stirred model. Overall, stereoselective glucuronidation was the principal metabolic pathway of ornidazole in humans. Furthermore, UGT1A9 and 2B7 were the predominant UGT isoforms responsible for R- and S-ornidazole glucuronidation in humans, respectively.