Losartan

How it works

It selectively blocks the angiotensin II type 1 receptor, causing vasodilatation, reduced aldosterone secretion and lower blood pressure without the bradykinin accumulation seen with ACE inhibitors.

Prescribing in practice

• It is contraindicated in pregnancy because angiotensin system blockers cause foetal renal and other malformations, so stop and seek alternatives if pregnancy is planned or confirmed.
• Risk of hyperkalaemia and renal impairment increases with potassium supplements, potassium-sparing diuretics, other renin-angiotensin drugs and NSAIDs.
• Avoid combining with an ACE inhibitor or aliskiren, and use caution in renovascular disease and volume depletion.

Monitoring

Check renal function and serum potassium before starting and after initiation or dose changes, and monitor blood pressure.

Counselling the patient

• Tell your clinician straight away if you become pregnant or are planning pregnancy.
• Avoid potassium-containing salt substitutes and over-the-counter anti-inflammatory painkillers unless advised.
• A small rise in blood test markers of kidney function can be expected when starting.

Evidence & guidelines

The LIFE and RENAAL trials support losartan for cardiovascular protection and diabetic nephropathy, consistent with NICE hypertension guidance.