Published: Journal of Analytical Toxicology, Volume 23, Number 4, July/August 1999, pp.242-246.
The Elimination Profiles of Oxaprozin in Equine Urine and
Serum after a 4.8-g Dose
Amanda Marland, Pratibha Sarkar, Randy Leavitt, Edward Lee-Ruff, and Jailall
Ramnauth
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 µg/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 µg/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 µg/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.Reproduction of editorial content of this
journal is prohibited without publisher’s permission.
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