A method for the extraction of diazepam and its metabolites (nordiazepam, temazepam, and oxazepam) from equine urine and serum and their quantitation and confirmation by liquid chromatography-tandem mass spectrometry is presented. Valium, a formulation of diazepam, was administered at a dose of 10 mg intramuscularly to four standard-bred mares. Diazepam is extensively metabolized in the horse to nordiazepam, temazepam, and oxazepam. Diazepam urinary concentrations were found to be less than 6 ng/mL. Nordiazepam was found to be mainly in its glucuronide-conjugated form and was measured out to a collection time of 53-55 h. Oxazepam and temazepam were entirely conjugated, and their urinary concentrations were measured out to collection times of 121 h and 77-79 h, respectively. Diazepam and nordiazepam were measured in equine postadministration serum out to collection times of 6 and 54 h, respectively. Oxazepam and temazepam were not detected in postadministration serum.

Tenoxicam (Mobiflex) was administered orally to four standardbred mares at a dose of 200 mg. Elimination profiles of tenoxicam and hydroxytenoxicam were generated based on quantitation of these analytes in urine and serum by liquid chromatography (LC) with ultraviolet detection. Tenoxicam was confirmed by LC-tandem mass spectrometry daughter ion mass spectra in the last postadministration sample in which tenoxicam was detected. The tenoxicam and hydroxytenoxicam urinary elimination profiles had the same shape for the same horse; however, each horse was significantly different from the others. One horse (Horse 15) showed a much broader and flatter elimination profile than the other horses. Each horse had a peak in analyte concentration at different collection times. The latest detection for both tenoxicam and hydroxytenoxicam was 29-31 h for all horses. The urinary tenoxicam limit of detection (LOD) and limit of quantitation (LOQ) were 0.3 and 0.4 microg/mL, respectively. The urinary hydroxytenoxicam LOD and LOQ were 0.6 and 0.8 microg/mL, respectively. Hydroxytenoxicam was found to be completely conjugated and tenoxicam completely unconjugated in equine urine. Serum elimination profiles of tenoxicam were measured to 120 h postadministration. Hydroxytenoxicam was not detected in postadministration serum. The last serum tenoxicam detection was at the 24-h collection time for all horses. The peak average concentration was 434.5 ng/mL at 3 h. The serum tenoxicam LOD and LOQ were 5.7 and 7.3 ng/mL.

A method for the extraction of oxaprozin from equine urine and serum and its quantitation by high-performance liquid chromatography-ultraviolet detection is presented. Confirmation of oxaprozin in postadministration extracts was accomplished by gas chromatographic- mass spectrometric analysis of methylated extracts or liquid chromatography with tandem mass spectrometry daughter ion mass spectra of underivatized extracts. Daypro, a formulation of oxaprozin, was administered orally at a dose of 4.8 g to four standardbred mares. Urine and serum samples were collected to 120 h postadministration. Base hydrolysis of equine urine before extraction resulted in an increase in the amount of oxaprozin measured, an indication of conjugation by ester formation. The urinary elimination profiles of each horse were significantly different from each other with more than one peak in oxaprozin concentration before the 29-31-h collection time. After this collection time, the differences between the oxaprozin urinary concentrations of each horse follow each other more closely. The peak average urinary concentrations of oxaprozin were 25.1 and 17.0 microg/mL at collection times of 8-10 and 18-22 h, respectively. The latest detection of oxaprozin in urine was at the last collection time of 119-121 h postadministration at a concentration close to the detection limit of approximately 0.1 microg/mL. The serum elimination profiles do not vary between horses as much as the urinary elimination profiles. The peak average serum concentration was 49.0 microg/mL at a collection time of 6 h postadministration. The latest detection was at the last collection time of 120 h. Oxaprozin is metabolized in the horse by hydroxylation. Two major urinary metabolites were isolated and identified as hydroxylated oxaprozin. The two urinary metabolites were isolated from equine postadministration urine and analyzed by mass spectrometry and proton nuclear magnetic resonance spectroscopy, which showed that the hydroxylation had occurred at the para positions of the two aromatic rings.

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