Source: Health Products Regulatory Authority (ZA) Revision Year: 2021 Publisher: Dr. Reddys Laboratories (Pty) Ltd., Block B, 204 Rivonia Road, Morningside, Sandton 2057
Pharmacological classification: 11.4.3 Medicines acting on the gastrointestinal tract – Other
Omeprazole is an inhibitor of the gastric proton pump (H+, K+-ATPase). It inhibits both basal and stimulated gastric acid secretion by parietal cells, whether induced by acetylcholine, gastrin or histamine.
Omeprazole has no effect on acetylcholine, histamine or gastrin receptors.
Orally administered omeprazole is well absorbed but to a variable extent. Absorption of omeprazole takes place in the small intestine and is usually completed within three to six hours. Bioavailability depends on dose and gastric pH and may reach 70% with repeated administration. Food has no influence on the bioavailability of omeprazole. Omeprazole is more than 95% bound to plasma proteins. Clearance from the circulation is by hepatic metabolism with a plasma half-life of 30 to 90 minutes. Hepatic metabolism occurs primarily via the cytochrome P450 (CYP) isoform (CYP2C19). The inactive metabolites are excreted mainly in the urine (80%) whilst the remaining 20% are excreted via the faeces. The average half-life of the terminal phase of the plasma concentration-time curve is approximately 40 minutes. There is no change in plasma half-life during treatment. The inhibition of acid secretion is related to the area under the plasma concentration-time curve (AUC) and not to the actual plasma concentration at a given time.
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