Determination of Methocarbamol in Equine Serum and Urine by High-Performance Liquid Chromatography with Ultraviolet Detection and Atmospheric Pressure Ionization-Mass Spectrometric Confirmation

Urine and serum samples collected from four standard-bred mares after an oral regimen administration of methocarbamol were extracted and analyzed. The method consisted of enzyme hydrolysis followed by a one-step liquid-liquid extraction, separation on a reversed-phase (RP-18) column, and detection using an ultraviolet (UV) detector. The confirmation was carried out using a liquid chromatography-atmospheric pressure ionization-mass spectrometry (LC-API-MS) system. Maximum methocarbamol concentrations of 1498, 1734, 1547, and 2322 µg/mL in urine and 4.9, 1.7, and 3.6 µg/mL in serum were observed. The peak concentrations of the drug were detected 1–4 h (urine) and 10–60 min (serum) after administration to four horses. The method validation results and drug elimination profiles for both urine and serum are presented and discussed.