RT Journal Article SR Electronic T1 Bioactivation of Diclofenac via Benzoquinone Imine Intermediates—Identification of Urinary Mercapturic Acid Derivatives in Rats and Humans JF Drug Metabolism and Disposition JO Drug Metab Dispos FD American Society for Pharmacology and Experimental Therapeutics SP 1608 OP 1613 VO 29 IS 12 A1 Grace K. Poon A1 Qing Chen A1 Yohannes Teffera A1 Jason S. Ngui A1 Patrick R. Griffin A1 Mathew P. Braun A1 George A. Doss A1 Christopher Freeden A1 Ralph A. Stearns A1 David C. Evans A1 Thomas A. Baillie A1 Wei Tang YR 2001 UL http://dmd.aspetjournals.org/content/29/12/1608.abstract AB The metabolism of diclofenac has been reported to produce reactive benzoquinone imine intermediates. We describe the identification of mercapturic acid derivatives of diclofenac in rats and humans. Three male Sprague-Dawley rats were administered diclofenac in aqueous solution (pH 7) at 50 mg/kg by intraperitoneal injection, and urine was collected for 24 h. Human urine specimens were obtained, and samples were pooled from 50 individuals. Urine samples were analyzed by liquid chromatography-tandem mass spectrometry (LC/MS/MS). Two metabolites with MH+ ions atm/z 473 were detected in rat urine and identified tentatively as N-acetylcysteine conjugates of monohydroxydiclofenac. Based upon collision-induced fragmentation of the MH+ ions, accurate mass measurements of product ions, and comparison of LC/MS/MS properties of the metabolites with those of synthetic reference compounds, one metabolite was assigned as 5-hydroxy-4-(N-acetylcystein-S-yl)diclofenac and the other as 4′-hydroxy-3′-(N-acetylcystein-S-yl)diclofenac. The former conjugate also was detected in the pooled human urine sample by multiple reaction-monitoring LC/MS/MS analysis. It is likely that these mercapturic acid derivatives represent degradation products of the corresponding glutathione adducts derived from diclofenac-2,5-quinone imine and 1′,4′-quinone imine, respectively. Our data are consistent with previous findings, which suggest that oxidative bioactivation of diclofenac in humans proceeds via benzoquinone imine intermediates. The American Society for Pharmacology and Experimental Therapeutics