Omeprazole

Omeprazole is an active substance belonging to the proton pump inhibitor class that inhibits gastric acid secretion. It is prescribed by physicians for conditions including gastroesophageal reflux disease and gastric and duodenal ulcers. At the end of March 2010, omeprazole 10 mg was approved in Switzerland for over-the-counter use in the short-term treatment of reflux symptoms such as heartburn and acid regurgitation. Subsequently, additional OTC medicines containing 20 mg were also approved. Omeprazole has a potential for drug interactions, for example with clopidogrel, because it inhibits CYP2C19. The most commonly observed adverse effects include gastrointestinal disturbances and headache. Omeprazole (ATC A02BC01) reduces gastric acid secretion by irreversibly (non-competitively) inhibiting the proton pump (H⁺/K⁺-ATPase) in the parietal cells of the stomach. It does not act locally in the gastric lumen but is absorbed in the intestine and reaches the parietal cells via the systemic circulation. It is a prodrug and is only converted to its active form by acid in the canaliculi of the parietal cells, where it binds covalently to the proton pump, thereby inhibiting it. Omeprazole is acid-labile and must be administered in enteric-coated dosage forms. Inhibition of gastric acid secretion is dose-dependent, and full effect is delayed, as with all proton pump inhibitors, occurring within approximately 4 days. Due to covalent binding, omeprazole is effective for considerably longer than its short half-life of less than one hour would suggest, and once-daily administration is therefore sufficient for most patients. Mechanism of action of proton pump inhibitors, click to enlarge. Illustration © PharmaWiki