Losartan with hydrochlorothiazide

How it works

Losartan blocks the angiotensin-II type 1 receptor to cause vasodilatation and reduce aldosterone-mediated sodium retention, while hydrochlorothiazide enhances renal sodium and water excretion, giving additive blood-pressure lowering.

Prescribing in practice

• The combination is contraindicated in pregnancy because the ARB component can cause serious foetal harm and must be discontinued as soon as pregnancy is detected.
• Avoid dual blockade of the renin-angiotensin system, and take care with potassium supplements or potassium-sparing diuretics because the combined potassium effect is unpredictable.
• Hydrochlorothiazide can provoke hyponatraemia, hypokalaemia, gout and photosensitivity, and is associated with a small increased risk of non-melanoma skin cancer.

Monitoring

Monitor blood pressure, renal function and serum electrolytes (sodium and potassium) before and during treatment, especially after dose adjustment or intercurrent illness.

Counselling the patient

• Do not take this medicine if you are or might become pregnant, and tell your doctor straight away if you conceive.
• Protect your skin from strong sunlight while on the diuretic component.
• Report dizziness, muscle cramps or unusual thirst, which can indicate a salt or water imbalance.

Evidence & guidelines

Combining an ARB with a thiazide diuretic for blood pressure uncontrolled on monotherapy aligns with NICE hypertension guidance and established trial evidence for the class.