Disposition of human drug preparations in the horse. V. Orally administered oxprenolol.

This research paper investigates the disposition of oxprenolol, a beta-blocker drug often used in human medicine, in horses after oral administration. Using advanced chemical methods, the researchers measured the levels of the drug and its metabolites in the horse’s urine over time, which helps understand how the horse’s body processes the drug.

Methodology

• Five horses that had fasted were orally administered with a dose of 160 mg oxprenolol.
• The urinary concentrations of oxprenolol and its significant human metabolites were determined.
• The quantitation was performed through a technique called gas chromatography-mass spectrometry (GC-MS), specifically in the selected ion mode (SIM).
• The researchers monitored ion m/z 466 of the heptafluorobutyric derivatives, to identify and quantify the presence of oxprenolol and its metabolites in the urine samples.

Findings

• Oxprenolol could be detected in the horse’s urine within 2 hours after administration and remained detectable for up to 24 hours.
• The maximum concentrations and excretion rates of oxprenolol in the urine happened between 2 and 12 hours after dosage.
• By 12 hours after administration, only 2.8% of the administered dose was excreted as conjugates of oxprenolol and major human metabolites.
• The major metabolites included 4-OH-oxprenolol and 5-OH-oxprenolol.
• These metabolites were detectable in the horse’s urine for up to 48 hours after dosage.

Significance

• This study provides valuable insight into how the horse’s body deals with orally administered oxprenolol.
• Such knowledge is crucial for understanding the potential effects, therapeutic dosage, and detection window of this drug (and similar drugs) in the horse’s body – essential information for both equine medicine and horse racing regulators.
• The methodology used here can also be applied to investigate the disposition of other drugs in horses or other animals, contributing to the broader field of veterinary pharmacology.