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.

A study of the effects of intravenous administration of either 150 mg or 250 mg of furosemide to standardbred mares pre-treated with other drugs was undertaken to determine whether a unique pattern of drug elimination into urine and from plasma for each compound occurred. Furosemide significantly reduced the plasma concentrations of codeine compared to control 2-6 h after furosemide administration. In contrast, the plasma concentrations of theophylline, phenylbutazone, pentazocine, guaifenesin and flunixin were not markedly altered by furosemide. In the case of acepromazine, clenbuterol and fentanyl, the data generated were insufficient to state with certainty whether or not furosemide affected the plasma concentrations of these three drugs. A significant reduction was noted in the urinary concentrations of guaifenesin, acepromazine, clenbuterol, phenylbutazone, flunixin, fentanyl and pentazocine within 1-4 h of furosemide administration. The urinary concentrations of theophylline remained reduced as long as 8 h after furosemide injection. Furosemide administration to horses pre-treated with codeine resulted in depression of urinary morphine concentrations 2-4 h and 9-12 h after furosemide injection. A lower furosemide dose (150 mg) produced changes in drug urinary excretion and plasma elimination equivalent to the higher dose (250 mg). It is evident that furosemide affects the urinary and plasma concentrations of other co-administered drugs but not in a predictable fashion, which limits the extrapolation of these results to as yet untested drugs.

No abstract

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.

Nimesulide is a nonsteroidal anti-inflammatory drug recently detected in equine blood and urine samples taken at the race track. The detection of the drug in a blood sample led to the identification of an unknown thin-layer chromatographic (TLC) spot in track urine samples as a metabolite of nimesulide. Characterization of the unknown TLC spot and comparison with the synthesized compound shows that the unknown TLC spot is a previously unreported equine metabolite of nimesulide. The metabolite was identified as resulting from the reduction of the nitro group on nimesulide to an amino group. This reduced nitro metabolite (4-amino-2-phenoxy-methanesulfonanilide) is a major metabolite of nimesulide in the equine.