The elimination profiles of oxaprozin in equine urine and serum after a 4.8-g dose.

The study focuses on the elimination profiles of a drug called oxaprozin in horse urine and blood serum after administering a dosage of 4.8 g. Different methods of extraction, quantitation, and confirmation of the drug’s presence were used. The study also found that oxaprozin is metabolized in horses through hydroxylation, resulting in hydroxylated oxaprozin.

Methodology

• A drug called oxaprozin was extracted from horse urine and blood serum. The extraction was quantified using a technique called high-performance liquid chromatography-ultraviolet detection.
• The presence of oxaprozin was confirmed through two methods. First, by using gas chromatographic-mass spectrometric analysis of methylated extracts. Second, by using liquid chromatography with tandem mass spectrometry daughter ion mass spectra of underivatized extracts.

Experiment and Results

• Oxaprozin, under the brand name Daypro, was administered orally at a dose of 4.8 g to four standardbred mares. Urine and blood serum samples were collected for up to 120 hours after administration.
• The study found that performing base hydrolysis of horse urine before extraction led to an increase in the amount of oxaprozin measured. This indicated conjugation through ester formation, a specific chemical reaction.
• The elimination profiles of the drug through urine were significantly varied among the horses, with more than one peak in oxaprozin concentration before the 29-31 hour collection time. After this period, the differences between each horse’s urinary concentration of the drug started to align more closely.

Drug Elimination

• The study found that oxaprozin was detectable up to the last collection time of 119-121 hours post-administration, almost touching the detection limit of approximately 0.1 microg/mL.
• In contrast to the varied urinary profiles, the elimination of the drug through the bloodstream was found to be more consistent among the horses. The peak average concentration in serum was 49.0 microg/mL collected 6 hours after administration, and it was detectable till the last collection time of 120 hours.

Oxaprozin Metabolism

• Further, the study found that horses metabolize the drug through a process called hydroxylation. The metabolized form of oxaprozin was identified as hydroxylated oxaprozin.
• Two major metabolites of the drug were isolated from the urine and were further analyzed using mass spectrometry and proton nuclear magnetic resonance spectroscopy. The results showed that the hydroxylation occurred at the para positions of the two aromatic rings.