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

• Published in: Journal of veterinary pharmacology and therapeutics Vol. 40; no. 1; pp. 92 - 96
• Main Authors: Knych, H. K., Stanley, S. D., Arthur, R. M., McKemie, D. S.
• Format: Journal Article
• Language: English
• Published: England 01.01.2017
• Subjects: Administration, Oral; Animals; Anti-Ulcer Agents - administration & dosage; Anti-Ulcer Agents - blood; Anti-Ulcer Agents - pharmacokinetics; Cimetidine - administration & dosage; Cimetidine - blood; Cimetidine - pharmacokinetics; Drug Administration Schedule - veterinary; Female; Half-Life; Horses - metabolism; Male; Omeprazole - administration & dosage; Omeprazole - blood; Omeprazole - pharmacokinetics; Physical Conditioning, Animal; Ranitidine - administration & dosage; Ranitidine - blood; Ranitidine - pharmacokinetics
• ISSN: 0140-7783; 1365-2885
• DOI: 10.1111/jvp.12328

The use of anti‐ulcer medications, such as cimetidine, ranitidine, and omeprazole, is common in performance horses. The use of these drugs is regulated in performance horses, and as such a withdrawal time is necessary prior to competition to avoid a medication violation. To the authors' knowledge, there are no reports in the literature describing repeated oral administrations of these drugs in the horse to determine a regulatory threshold and related withdrawal time recommendations. Therefore, the objective of the current study was to describe the disposition and elimination pharmacokinetics of these anti‐ulcer medications following oral administration to provide data upon which appropriate regulatory recommendations can be established. Nine exercised Thoroughbred horses were administered 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. Blood samples were collected, serum drug concentrations were determined, and elimination pharmacokinetic parameters were calculated. The serum elimination half‐life was 7.05 ± 1.02, 7.43 ± 0.851 and 3.94 ± 1.04 h for cimetidine, ranitidine, and omeprazole, respectively. Serum cimetidine and ranitidine concentrations were above the LOQ and omeprazole and omeprazole sulfide below the LOQ in all horses studied upon termination of sample collection.