Olmesartan medoxomil

How it works

It selectively blocks the angiotensin II type 1 (AT1) receptor, preventing angiotensin II-mediated vasoconstriction and aldosterone secretion to lower blood pressure.

Prescribing in practice

• It can rarely cause a severe sprue-like enteropathy (chronic diarrhoea with marked weight loss and intestinal villous atrophy), sometimes after months or years — investigate other causes and discontinue if no other cause is found, as symptoms resolve on stopping.
• Avoid in pregnancy because of fetal toxicity; women planning pregnancy should be switched to an alternative.
• Hyperkalaemia and reduced renal function can occur, especially with renal impairment, renal artery stenosis, or alongside potassium-sparing diuretics, potassium supplements or NSAIDs; symptomatic hypotension may occur in volume-depleted patients.

Monitoring

Check renal function, electrolytes (including potassium) and blood pressure before starting and after initiation or dose changes. Monitor blood pressure for response, and consider olmesartan as a cause in any patient who develops chronic diarrhoea and weight loss.

Counselling the patient

• Report persistent or severe diarrhoea with weight loss, as the medicine may occasionally cause this and may need to be stopped.
• Tell us at once if you become pregnant or are planning pregnancy, as this medicine must be stopped.
• Avoid potassium-based salt substitutes and do not start potassium supplements unless advised.

Evidence & guidelines

ARBs are a guideline-recommended option for hypertension (NICE NG136); sprue-like enteropathy is an MHRA-recognised class warning for olmesartan.