Pharmacokinetics of intravenous, plain oral and enteric‐coated oral omeprazole in the horse

The objectives were to document the pharmacokinetics of intravenous, enteric‐coated oral and plain oral omeprazole in fasted horses and to investigate the impact of feeding on the bioavailability of an enteric‐coated omeprazole. Twelve horses received four treatments: intravenous omeprazole (0.5 mg/kg) in the fasted state ( IV ‐Fasted), enteric‐coated omeprazole (4 mg/kg) orally in the fasted state ( ECO ‐Fasted), enteric‐coated omeprazole (4 mg/kg) orally in the fed state ( ECO ‐Fed) and plain omeprazole (4 mg/kg) orally in the fasted state ( PL ‐Fasted). Plasma omeprazole concentrations were determined by UHPLC ‐ MS . Bioavailability was higher ( P  = 0.038) in the ECO ‐Fasted group (21.5 [9.0–27.7]%) than the PL ‐Fasted group (10.1 [7.7–13.3]%). Similarly, AUC 0‐∞ was higher in the ECO ‐Fasted group than the PL ‐Fasted group ( P  = 0.027). No significant differences were present between the ECO ‐Fasted and ECO ‐Fed groups with regards to bioavailability, C max , T max or AUC 0‐∞ . When the half‐life data from the oral formulations was pooled, it was longer than that observed in the IV ‐Fasted group (100 [73–118] min) and 35 [34‐39] min, respectively; P  < 0.0001). Bioavailability of enteric‐coated omeprazole was higher than previously reported and feeding had minimal impact. Bioavailability of plain omeprazole was approximately half that of enteric‐coated omeprazole. The longer half‐life observed following oral administration was consistent with the flip‐flop effect and has not previously been described for omeprazole in the horse.