Quantification of unconjugated and total ibuprofen and its metabolites in equine urine samples by gas chromatography–tandem mass spectrometry: Application to the excretion study

Abstract

Ibuprofen (IBU) is a widely used nonsteroidal anti-inflammatory drug (NSAID) in human and also veterinary medicine. NSAIDs are usually highly metabolized compounds in horses; they are often present in equine urine, mostly in their conjugated forms (glucuronides). Thus, hydrolysis to cleave the glucuronide linkage prior to anti-doping analysis is often necessary for improving detection. In this study, unconjugated and total IBU and its metabolites were determined by GC–MS/MS in equine urine samples collected after drug administration to six horses (mares and geldings). The results indicated that enzymatic hydrolysis using β-glucuronidase from E. coli improved the detection of IBU and its phase I metabolites in equine urine samples; in a few cases, this method allowed to monitor analytes for a longer period of time. The percentages of conjugated analytes were within 5.4–48.4% for IBU and in the range of 0.2–55.5% for phase I metabolites of IBU. Unchanged IBU was found at the highest concentration levels in equine urine samples collected after drug administration; and also parent compound lasted for a longer period of time in equine urine than its phase I metabolites, with the exception of samples collected from one horse, in which 2-OH IBU was detectable for a longer duration than IBU.