omeprazole

Omeprazole is a proton pump inhibitor (PPI) used to reduce gastric acid production. It is a prodrug that is activated in the acidic environment of gastric parietal cell canaliculi, where it binds irreversibly to the H+/K+-ATPase enzyme, suppressing acid secretion. The onset of action is typically within an hour, with acid suppression lasting up to 24 hours after a daily dose.

Indications include gastroesophageal reflux disease (GERD) with or without esophagitis, maintenance therapy for erosive esophagitis, treatment and prevention of peptic ulcers (including those caused by NSAIDs), treatment of Zollinger-Ellison syndrome, and as part of eradication regimens for Helicobacter pylori in combination with antibiotics.

Common dosing for adults is typically 20 mg once daily for GERD, with higher or twice-daily dosing for erosive disease or ulcers. Therapy is often short-term but may be longer for chronic conditions. Formulations include oral delayed-release capsules and tablets and intravenous formulations for hospital use.

Omeprazole is mainly metabolized by the liver via the cytochrome P450 system, particularly CYP2C19 and, to a lesser extent, CYP3A4. Because of metabolism, there are potential drug interactions, notably with clopidogrel, where omeprazole may affect the activation of clopidogrel; other interactions relate to drugs whose absorption depends on gastric pH.

Common adverse effects are usually mild and include headache, diarrhea, nausea, abdominal pain, and constipation. Long-term use has been associated with magnesium deficiency, vitamin B12 deficiency, infections of the gastrointestinal tract, and an increased risk of fractures and pneumonia, with risk rising with duration of therapy.

Brand names include Prilosec and Losec. Omeprazole is available by prescription and over the counter in many jurisdictions.