Oral bioavailability of omeprazole before and after chronic therapy in patients with duodenal ulcer.

1. This study investigated the mechanism of the increase in oral bioavailability of omeprazole during repeated oral dosing. Eight patients with duodenal ulcer received an i.v. dose of omeprazole before and after a 4-week course of oral omeprazole, 20 mg daily, given as enteric-coated granules. 2. AUCoral and oral bioavailability (F) increased during omeprazole treatment by 50% (P less than 0.01) and 35% (P less than 0.05), respectively. 3. There was no change in the systemic clearance of omeprazole after i.v. dosage following the course of treatment. 4. We conclude that the increased omeprazole AUC observed on repeated administration of enteric-coated granules is due to increased systemic availability rather than decreased systemic elimination. The increased availability appears to be due to increased gastrointestinal absorption rather than decreased first-pass hepatic extraction.