Safety, acceptability and endoscopic findings in foals and yearling horses treated with a paste formulation of omeprazole for twenty-eight days.

Abstract: A paste formulation of the H+,K(+)-ATPase inhibitor omeprazole was evaluated in Thoroughbred foals and yearlings for its safety and acceptability. Twenty foals age 11-16 weeks and 20 yearling horses age 15-17 months were included and gastroscopic examinations performed 1-3 days before and at the end of each trial. Lesions were scored on a scale of 0 to 3 and animals allocated based on endoscopic lesion score and sex, with 4 animals in each of 5 replicates. Dosages of 4 mg omeprazole/kg bwt or sham treatment were administered once daily for 28 days, from a syringe graduated in 50 lb (22.68 kg) increments, the amount of paste administered being rounded up to the nearest corresponding weight in pounds. Acceptability of the paste or sham treatment was assessed and recorded by the individual administering the treatment on the basis of the tolerance or resistance to insertion of the syringe into the mouth, administration of the paste and if the paste was swallowed or actively expelled by the animal. Safety was determined on the basis of daily observation recordings and physical examination findings during and at the conclusion of the trial. Treatment was judged to have been accepted for all 420 doses of omeprazole paste and all 140 sham doses given to foals during the trial and for 418/420 doses of paste and all 140 sham doses given to yearlings. Two doses of paste were entirely rejected by yearlings. On the initial endoscopic examination, lesions were observed in the gastric squamous epithelial mucosa in 4 foals and 3 yearlings, and single small, superficial erosions were seen in the gastric glandular mucosa of 2 foals. On the second examination there were small, superficial erosions in the squamous mucosa in 3 foals and 2 yearlings, multi-focal superficial erosions in 1 foal and 1 yearling, and 1 foal had large areas of erosion extending from the margo plicatus toward the dorsal fundus. No lesions in the glandular mucosa were seen in foals or yearlings. There were no significant differences (P < 0.05) in lesion scores between the beginning and the end of the trials in the omeprazole-treated or sham-treated groups of foals or yearlings. A paste formulation of omeprazole, administered at a dose of 4 mg/kg bwt once daily for 28 days, was determined to be highly acceptable to the foals and yearlings we studied, and no adverse effects attributable to the medication were noted.