Omepac Mechanism of Action

Pharmacology: Capsule: Mechanism of Action: OMEPAC 20 (omeprazole) is substituted benzimidazole derivative which markedly inhibits basal and stimulated gastric acid secretion by a unique mode of action, specifically blocking the H⁺/ K⁺ATPase enzyme system of the gastric parietal cell (the so called proton pump) which is the terminal step in the acid secretory pathway. It has a quick onset of action and when the drug is discontinued, secretory activity returns gradually over 3 to 5 days.
Injection: Omeprazole is a proton pump inhibitor. It inhibits secretion of gastric acid by irreversibly blocking the enzyme system of hydrogen/potassium adenosine triphosphate (H⁺/K⁺ATPase), the "proton pump" of the gastric parietal cell.
Pharmacokinetics: Capsule: Omeprazole is rapidly absorbed, but to a variable extent, following oral administration.
Absorption of omeprazole is not affected by food but is dose dependent. 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 markedly affected in patients with renal impairment. Following absorption, Omeprazole is almost completely metabolised in the liver by cytochrome P 450 isoforms and rapidly eliminated, mostly in the urine. Although the elimination half-life from plasma is short, being reported to be about 0.5 to 3 hours, its duration of action with regard to inhibition of acid secretion is much longer allowing it to be used in single daily doses. Omeprazole is highly bound (about 95%) to plasma proteins.
Injection: The absorption of Omeprazole appears to be dose-dependent; increasing the dosage above 40 mg has been reported to increase the plasma concentrations. In addition, absorption is higher after a 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 CYP3A to form Omeprazole sulfone. The metabolites are inactive, and are excreted mostly in the urine and to a lesser extent in 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.