Plasma and Urine Pharmacokinetics of Long-Acting Injectable Omeprazole Following Intramuscular Administrations to Healthy Thoroughbred Horses.

The research article presents a pharmacokinetic study on a long-lasting injectable form of Omeprazole, an anti-ulcer drug, conducted on six Thoroughbred horses. The drug remains detectable in a horse’s plasma and urine for over 16 days after a single weekly injection, challenging its feasible application in competitive horse racing.

Objective and Methodology of the Study

• The research aimed to assess the detection time (DT) of long-acting injectable Omeprazole, a popular anti-ulcer medication, in the plasma and urine of healthy Thoroughbred horses compared to the International Screening Limit (ISL) — a predetermined timeframe the drug should stay detectable in the body.
• The interest in the pharmacokinetics of injectable Omeprazole arose following the release of a new formulation for the drug that can be administered intramuscularly.
• To evaluate the DT, six Thoroughbred horses were administered four weekly doses of injectable Omeprazole at 4mg/kg. Plasma and urine concentrations of Omeprazole were then measured using liquid chromatography-tandem mass spectrometry — an analytical technique designed to find, quantify, and identify particles in a sample.

Results of the Study

• The results revealed that the DT for the long-acting Omeprazole formulation surpassed 384 hours or 16 days in both plasma and urine. This duration exceeds the established ISL of 48 hours post-consumption, by which racing horses should have completely metabolized the substance to avoid detection.
• This finding challenges the practicality of administering this long-acting injectable medication to competitive horses in training. Despite the convenience of administering a once-weekly injection compared to daily oral administration, the longer DT could potentially violate horse racing rules if used within a competitive window.

Implications of the Findings

• Given the drug’s prolonged detectability, it is less likely to be used for horses actively in training or expecting to compete in races.
• Despite the longer DT, the study concluded the injectable drug could still be therapeutically beneficial for horses not involved in racing or during their off-training periods.
• The traditional oral formulation of Omeprazole could still be validly used during active horse training, given its shorter DT within the ISL. It thereby upholds compliance with racing rules while providing the necessary treatment for potential gastric ailments.