RT Journal Article SR Electronic T1 Isolation, Purification, and Structural Characterization of Flunixin Glucuronide in the Urine of Greyhound Dogs JF Drug Metabolism and Disposition JO Drug Metab Dispos FD American Society for Pharmacology and Experimental Therapeutics SP 294 OP 298 VO 26 IS 4 A1 Thomas C. Brady A1 Albert J. Kind A1 Walter H. Hyde A1 Mark Favrow A1 Dennis W. Hill YR 1998 UL http://dmd.aspetjournals.org/content/26/4/294.abstract AB A urinary metabolite of flunixin in greyhound dogs was isolated and purified by a gradient-elution solid-phase extraction technique. The purified metabolite was shown to be hydrolyzed to free flunixin by strong base and by β-glucuronidase, suggesting the presence of a C1-β-glucuronide ester of flunixin. The metabolite was further characterized by positive-ion, tandem MS with electrospray ionization. Mass spectral data showed the presence of a protonated molecular ion (M+1) at m/z 473, which was consistent with the molecular weight of protonated flunixin glucuronide, and a product ion atm/z 297, which was consistent with the molecular weight of protonated flunixin. Collisionally induced dissociation of them/z 297 product ion showed a fragmentation pattern consistent with that of standard flunixin. These data support the contention that this metabolite of flunixin in greyhound urine is the C1-β-glucuronide of flunixin. Acyl glucuronide metabolites of some organic acid drugs have been shown to bind covalently to tissue proteins in vitro, in vivo, and ex vivo. The presence of this metabolite may, therefore, have pharmacokinetic and pharmacodynamic implications for flunixin in greyhound dogs, as well as in other animal species in which the acyl glucuronide of flunixin is a metabolite. The American Society for Pharmacology and Experimental Therapeutics