Adults

For duodenal ulcer and GERD: 20 mg once daily for 4-8 weeks. For gastric ulcer: 20 mg once daily for 4-8 weeks. For Zollinger-Ellison Syndrome: Initial dose 60 mg once daily, adjusted as needed. For H. pylori eradication: 20 mg twice daily in combination with antibiotics for 7-14 days.

Elderly

No specific dose adjustment is generally required for elderly patients, but caution is advised in patients with severe hepatic impairment.

Renal_impairment

No dose adjustment is necessary for patients with impaired renal function.

Onset

Acid-suppressive effect begins within 1 hour after oral administration, with maximum effect observed within 2 hours. Full therapeutic effect is achieved within a few days.

Excretion

Approximately 80% of omeprazole metabolites are excreted in the urine, and about 20% are excreted in the feces.

Half life

Plasma elimination half-life is approximately 0.5 to 1 hour, but the duration of acid suppression is much longer due to irreversible binding to the proton pump.

Absorption

Rapidly absorbed from the gastrointestinal tract, with peak plasma concentrations occurring within 0.5 to 3.5 hours. Bioavailability increases with repeated dosing.

Metabolism

Extensively metabolized in the liver primarily by the cytochrome P450 enzyme system, mainly CYP2C19 and CYP3A4.

Digoxin

Increased absorption and plasma levels of digoxin have been observed, necessitating monitoring.

Warfarin

Increased INR and prothrombin time have been reported with co-administration, requiring careful monitoring.

Nelfinavir

Concomitant use is contraindicated due to a significant decrease in nelfinavir plasma levels.

Clopidogrel

Omeprazole may reduce the antiplatelet effect of clopidogrel by inhibiting its conversion to the active metabolite. Concomitant use should be avoided.

Methotrexate

Omeprazole may increase methotrexate levels, especially in high-dose therapy, leading to potential toxicity.