Quantitative determination of carisoprodol and its metabolites in equine urine and serum by liquid chromatography-tandem mass spectrometry

A liquid chromatography-tandem mass spectrometry (LC-MS-MS) method was developed for the quantitation of carisoprodol and its metabolites, meprobamate and hydroxycarisoprodol, in equine urine and serum. The method consists of solid phase extraction followed by LC-MS-MS using electrospray ionization (ESI) and multiple reaction monitoring. Validation of the method showed excellent sensitivity, selectivity, accuracy, precision and ruggedness. The urinary excretion and serum profiles of these analytes were determined after oral administration of carisoprodol and meprobamate. The determination of hydroxycarisoprodol in urine and/or intact carisprodol in serum allows one to effectively distinguish between specimens arising from administration of carisoprodol (a class 4 drug violation) and meprobamate (a class 2 violation).