Disposition of the anti-ulcer medications ranitidine, cimetidine, and omeprazole following administration of multiple doses to exercised Thoroughbred horses.

This research investigates the processing and expulsion dynamics of common anti-ulcer medications—cimetidine, ranitidine, and omeprazole—in racing horses following repeated dosage. The study was conducted to create evidence-based regulatory guidelines for administering these drugs, ensuring their complete elimination from the horse’s system before competition to prevent medication-related violations.

Objective and Background

The study was centered on determining the elimination pharmacokinetics (how the horse’s body processes and eliminates the drugs) of three widely-used anti-ulcer drugs—cimetidine, ranitidine, and omeprazole—in performance horses.

• Performance horses are often administered these drugs to manage ulcer issues, but such medications are regulated in the sport.
• Since a breach of the medical code may result in penalties during competitions, it is crucial to have a scientifically-backed withdrawal time before the competition.
• However, previous literature has not described the repercussions of repeated administrations of these drugs in horses, posing a gap in knowledge related to their regulatory thresholds and withdrawal recommendations.

Methodology

The experimentation was carried out on nine vigorously trained Thoroughbred horses.

• Each horse was administered multiple doses of 20 mg/kg BID of cimetidine or 8 mg/kg BID of ranitidine, both for seven doses, or 2.28 g of omeprazole SID for four doses.
• Following the administration of the drugs, blood samples of the horses were taken and tested for serum drug concentrations.
• The elimination pharmacokinetic parameters were calculated based on the gathered results.

Findings

The results showed significant variation among the chairmen half-lives—time needed by the body to clear half of the drug amount—of the three drugs tested.

• For cimetidine, the serum elimination half-life was 7.05 ± 1.02 hours
• For ranitidine, the serum elimination half-life was 7.43 ± 0.851 hours
• For omeprazole, the serum elimination half-life was 3.94 ± 1.04 hours
• Upon termination of sample collection, the serum concentrations for cimetidine and ranitidine were above the Lower Limit of Quantitation (LOQ), signifying their gradual and slower clearance from the body.
• In contrast, the concentrations of omeprazole and omeprazole sulfide were below the LOQ, pointing towards their quicker elimination from the horse’s body.

These results are critical for setting the appropriate administration schedules as well as withdrawal timelines for these drugs among racing horses.