Gastrec 40 Mechanism of Action

Pharmacology: Omeprazole belongs under a class of drugs called proton pump inhibitors. Omeprazole blocks or inhibits gastric acid secretions. It reduces gastric acid secretion by inhibiting the enzyme system of hydrogen-potassium adenosine triphosphate, which is regarded as the acid proton pump of the gastric parietal cells. Also called H⁺/K⁺-Atpase, the enzyme is responsible for the exchange of hydrogen and potassium ions during the formation of hydrochloric acid.
Pharmacokinetics: Omeprazole is rapidly but variably absorbed following oral administration. Absorption is not affected by food. Omeprazole is acid-labile. The absorption of omeprazole appears to be dose-dependent. Increasing the dosage above 40 mg has been reported to increase the plasma concentrations in a non-linear fashion because of saturable first-pass hepatic metabolism. In addition, absorption is higher after long-term administration. Bioavailability of omeprazole may be increased in elderly patients, in some ethnic groups such as Chinese, and in patients with impaired hepatic function, but is not markedly affected in patients with renal impairment. Following absorption, omeprazole is almost completely metabolized in the liver, primarily by the cytochrome P450 isoenzyme CYP2C19 to form hydroxyomeprazole, and to a small extent by CYP3A4 to form omeprazole sulfone. The metabolites are inactive, and are excreted mostly in the urine and to a lesser extent in the bile. The elimination half-life from plasma is reported to be about 0.5 to 3 hours. Omeprazole is highly bound (about 95%) to plasma proteins.