Effect of omeprazole on gastric acid secretion and plasma gastrin in man.

Single doses of omeprazole inhibit pentagastrin-stimulated gastric acid secretion and almost complete inhibition can be achieved for 4-6 hours with a single dose of 80 mg. Acid secretion then slowly returns and reaches normal levels after 3-4 days. Omeprazole also dose-dependently inhibits basal acid secretion as well as acid secretion stimulated with histamine, peptone and modified sham feeding, with similar efficiency. During repeated once-daily dosing with an enteric-coated granule capsule formulation, inhibition of acid secretion increased initially, and stabilized within about 4 days. Dose-response studies in patients with duodenal ulcers and healthy subjects have shown that 20-40 mg/day results in a peak reduction (80-100%) of pentagastrin-stimulated acid secretion 6 hours after dose. Studies of 24-hour intragastric acidity in duodenal ulcer patients have shown that 4 weeks of treatment with omeprazole, 20 mg once daily, resulted in a reduction of median intragastric acidity by 97%, which was superior to the 57% median reduction achieved with ranitidine, 150 mg b.d., for 4 weeks in the same patients. During omeprazole treatment, fasting plasma gastrin increased in relation to the degree of inhibition of acid secretion. After discontinuation of treatment, plasma gastrin normalized. Treatment with omeprazole, 20 mg, increased 24-hour plasma gastrin to the same extent as after highly selective vagotomy. Long-term treatment with omeprazole, 20-40 mg, for up to 2 years has not been associated with any progressive rise in fasting plasma gastrin.