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Proton Pump Inhibitor.
Pharmacology: Omeprazole is a proton pump inhibitor (PPI) that belongs to the substituted benzimidazoles class of antisecretory compounds. It suppresses gastric acid secretion by specific inhibition of the H+/K+ ATPase enzyme system at the secretory surface of the gastric parietal cell. This enzyme system is regarded as the acid (proton) pump within the gastric mucosa hence, omeprazole has been characterized as a gastric acid-pump inhibitor, in that it blocks the final step of acid production. This effect is dose-related and leads to inhibition of both basal and stimulated acid secretion.
Pharmacokinetics: Bioavailability: Omeprazole's apparent volume of distribution is approximately 0.3 L/kg in healthy subjects and in patients with renal insufficiency. The volume of distribution is slightly decreased in elderly patients and in patients with hepatic insufficiency. Omeprazole is highly protein bound with about 95% bound to plasma proteins.
Omeprazole is completely metabolized mainly in the liver via the cytochrome P450 system (CYP). A major part of its metabolism is dependent on CYP2C19 (S-mephenytoin hydroxylase) which is responsible for the formation of hydroxyomeprazole, its major metabolite in the plasma. The average half-life after IV administration is approximately 40 minutes and total plasma clearance is 0.3 to 0.6 L/min.
About 80% of the metabolites are excreted in the urine and the remaining metabolites are seen in the feces. Patients with impaired liver function have increased elimination half-life; however, omeprazole has not shown any accumulation with once daily oral dosing.
