Omeprazole

Omeprazole is a proton pump inhibitor (PPI) that irreversibly blocks the hydrogen-potassium ATPase enzyme system (the proton pump) on the parietal cells of the gastric mucosa.

This produces a profound and sustained reduction in basal and stimulated gastric acid secretion.

Omeprazole is licensed for the treatment of gastro-oesophageal reflux disease (GORD), peptic ulcer disease (gastric and duodenal), Zollinger-Ellison syndrome, NSAID-associated ulceration, and as part of Helicobacter pylori eradication regimens.

A single 20 mg dose inhibits approximately 70% of maximal acid output, with full inhibition achieved after repeated daily dosing over 5 days.

Omeprazole is one of the most widely prescribed medications worldwide and is available over the counter at lower doses for short-term symptomatic relief of heartburn.

The BNF and NICE recommend PPIs as first-line acid suppression therapy for GORD and peptic ulcer disease. Long-term prescribing should be subject to regular clinical review.

Swallow capsules whole with a glass of water before a meal, ideally in the morning before breakfast for maximum efficacy, as the drug binds most effectively to actively secreting proton pumps stimulated by food.

Do not crush, chew, or open the gastro-resistant capsules.

If swallowing is difficult, capsules may be opened and the gastro-resistant granules mixed with a small amount of acidic fruit juice or yoghurt and swallowed immediately without chewing. For H.

pylori eradication, take omeprazole alongside the prescribed antibiotics as directed by your doctor. Complete the full course even if symptoms resolve early.

Long-term use should be reviewed at least annually by your prescriber.

GORD: 20 mg once daily for 4-8 weeks; maintenance 10-20 mg daily.

Duodenal ulcer: 20 mg once daily for 4 weeks (usually heals within 2 weeks).

Gastric ulcer: 20-40 mg once daily for 8 weeks.

H. pylori eradication: 20 mg twice daily for 7 days combined with two antibiotics (e.g. amoxicillin and clarithromycin per NICE recommendations).

Zollinger-Ellison syndrome: Initial dose 60 mg daily; adjust according to acid output.

NSAID prophylaxis: 20 mg once daily.

In severe hepatic impairment, do not exceed 20 mg daily. No dose adjustment is needed for renal impairment. Elderly patients generally do not require dose modification.

Side effects per SmPC frequency classification.

Common (≥1/100 to <1/10): Headache, abdominal pain, diarrhoea, constipation, flatulence, nausea, vomiting.

Uncommon (≥1/1,000 to <1/100): Dizziness, paraesthesia, sleep disturbance, dry mouth, elevated liver enzymes, rash, dermatitis, pruritus, urticaria, malaise.

Rare (≥1/10,000 to <1/1,000): Agranulocytosis, pancytopenia, interstitial nephritis, hepatitis (with or without jaundice), Stevens-Johnson syndrome, toxic epidermal necrolysis, taste disturbance, photosensitivity, arthralgia, myalgia, gynaecomastia.

Long-term use concerns (MHRA guidance): Prolonged PPI use (>1 year) is associated with hypomagnesaemia, increased fracture risk (hip, wrist, spine), Clostridioides difficile infection, vitamin B12 deficiency, and rebound acid hypersecretion on discontinuation.

The risk-benefit ratio should be reassessed regularly.

Long-term PPI use should be reviewed at least annually. The MHRA and NICE advise stepping down to the lowest effective dose or intermittent dosing where possible.

Exclude gastric malignancy before initiating treatment, as omeprazole may mask symptoms of gastric cancer.

Concomitant use with clopidogrel should be avoided where possible, as omeprazole inhibits CYP2C19 and reduces the antiplatelet effect of clopidogrel; lansoprazole or pantoprazole are preferred alternatives.

Chronic PPI use reduces calcium absorption and may increase fracture risk; ensure adequate dietary calcium and vitamin D.

Omeprazole interacts with methotrexate (delayed renal elimination) and phenytoin (increased plasma levels).

Monitoring of magnesium levels is recommended in patients on long-term therapy, particularly if concurrent with other drugs that deplete magnesium.

Omeprazole is contraindicated in patients with known hypersensitivity to omeprazole, other substituted benzimidazoles, or any excipient.

Concomitant use with nelfinavir is contraindicated due to significantly reduced nelfinavir plasma levels. Caution is needed but not absolute contraindication with atazanavir (reduced absorption).