Omeprazole

How it works

It irreversibly inhibits the H+/K+-ATPase (proton pump) on the luminal surface of gastric parietal cells, markedly reducing both basal and stimulated gastric acid secretion.

Prescribing in practice

• Long-term or high-dose use is associated with hypomagnesaemia, an increased risk of fractures and a small increased risk of Clostridioides difficile and other enteric infections; review the indication periodically and use the lowest effective dose.
• It is a CYP2C19 inhibitor and can raise levels of interacting drugs; co-prescription with clopidogrel may reduce clopidogrel's antiplatelet effect.
• Acid suppression can mask the symptoms of gastric malignancy, so investigate alarm features before and during treatment.

Monitoring

Check serum magnesium before and periodically during prolonged therapy, and review the ongoing need for treatment at regular intervals.

Counselling the patient

• Take before food, typically in the morning, and swallow capsules whole.
• Report new diarrhoea, muscle cramps or unexplained tiredness, which may indicate infection or low magnesium.
• Do not stop abruptly after long-term use without discussing a step-down with your prescriber.

Evidence & guidelines

Proton pump inhibitor efficacy in acid-related disease is well established and reflected in NICE dyspepsia and GORD guidance.