Pharmacokinetics and antisecretory effects of intravenous omeprazole in horses

Summary Eight young female horses with chronic gastric cannulae received 0.5 mg omeprazole/kg bwt iv once daily for 5 consecutive days. Gastric secretion was measured on the 1st and 5th day. Basal secretion was determined 1 h before and 1 h after the omeprazole dose, followed by pentagastrin stimulation for 2 h. Gastric juice samples were collected from the cannula every 15 mins for the determination of volume, pH, acidity, and acid outputs. As control, sterile water was similarly administered to all 8 horses. Pharmacokinetic evaluation of intravenous omeprazole was determined concurrently on the 1st and 5th day of administration. Omeprazole reduced both basal and stimulated acid output (mmol H+/h) by more than 90%, with a significant increase in gastric juice pH both on the 1st and 5th day of administration. A trend suggesting a long duration of inhibitory action was observed 23 h after the 4th dose of omeprazole since 58% of gastric acid output was inhibited. Thus omeprazole shows potential as a once a day antisecretory drug in horses. Plasma omeprazole concentration versus time profiles were best described using a two-compartment model. There was no statistical difference between the pharmacokinetic disposition of omeprazole on Days 1 and 5. The elimination half-life of intravenous omeprazole was about 30 mins.