Omeprazole (20 mg) daily given in the morning or evening: a comparison of effects on gastric acidity, and plasma gastrin and omeprazole concentration.

Although omeprazole has a long duration of action and has usually been given in the morning, there are theoretical advantages in administering antisecretory drugs in the evening as has been shown for the H2-receptor antagonists. The aim of this study was to compare the effects of placebo and 20 mg omeprazole given either in the morning or evening, on gastric acidity, plasma gastrin levels and plasma omeprazole in 6 duodenal ulcer patients. The 24-hour mean pH (+/- S.E.M.) was: placebo 1.7 +/- 0.1; morning doing, 3.9 +/- 1.8 (P less than 0.01); evening dosing, 2.9 +/- 1.1 (N.S.). There was a large inter-individual variability of intragastric acidity in response to omeprazole, which was reflected both in the plasma gastrin and in the area under the plasma omeprazole concentration-time curve. Morning administration of omeprazole is optimal, but variability in the patient response to 20 mg omeprazole is still seen.