The elimination profiles of tenoxicam and hydroxytenoxicam in equine urine and serum after a 200-mg oral dose.

This research article investigated how the drug Tenoxicam, along with its derivative hydroxytenoxicam, is eliminated from a horse’s system after an oral dose. Using liquid chromatography and mass spectrometry, researchers traced the presence of these substances in the urine and serum of four horses over a period of time.

Drug Administering and Testing Methods

• The research began by giving four standardbred mares a 200mg oral dose of Tenoxicam, which is a non-steroidal anti-inflammatory drug (NSAID), also known by the brand name Mobiflex.
• The traces of Tenoxicam and hydroxytenoxicam, a metabolite of Tenoxicam, were then tracked in each horse’s urine and blood serum using liquid chromatography with an ultraviolet detection method, a common technique for precise quantification of specific substances.
• The researchers also confirmed the presence of Tenoxicam using LC-tandem mass spectrometry, a more sensitive testing mechanism.

Elimination Profiles

• Each horse exhibited a unique elimination profile for both Tenoxicam and hydroxytenoxicam, with peak concentration times varying across individuals.
• Interestingly, the shape of the elimination profiles for Tenoxicam and hydroxytenoxicam in urine was identical within the same horse, but varied across different individuals. One horse in particular displayed a significantly more gradual and sustained elimination pattern.
• The final traceable amounts of both substances in urine were found between 29 and 31 hours after administration.

Drug Concentration

• The limits of detection (LOD) and limits of quantitation (LOQ) for Tenoxicam in urine were at very low concentrations, as were the LOD and LOQ for hydroxytenoxicam.
• The researchers also found that tenoxicam was fully unconjugated and hydroxytenoxicam was fully conjugated in horse urine.
• In serum, traces of Tenoxicam were detectable up to 120 hours after administration. Hydroxytenoxicam could not be found in the serum.
• The peak average concentration of Tenoxicam in serum was noted at three hours post-administration, with a value of 434.5 ng/mL.

These findings reflect how the equine body metabolizes and eliminates Tenoxicam, providing valuable insights for equine medicine, particularly in relation to dosing and detection times.