Hydrochlorothiazide

How it works

It inhibits the sodium-chloride co-transporter in the distal convoluted tubule, increasing urinary sodium and water loss and, with chronic use, lowering peripheral vascular resistance.

Prescribing in practice

• It can cause electrolyte disturbances, particularly hypokalaemia and hyponatraemia, so electrolytes should be checked and patients monitored, especially in the elderly.
• An MHRA alert has highlighted a cumulative-dose-related risk of non-melanoma skin cancer, and patients should be advised on sun protection and to report new or changing skin lesions.
• It may unmask or worsen gout and can affect glucose and lipid control; use with caution in renal or hepatic impairment.

Monitoring

Monitor serum electrolytes, renal function and blood pressure, particularly after initiation and in older or at-risk patients.

Counselling the patient

• Use sun protection and report any new, changing or non-healing skin lesions.
• Report symptoms of low electrolytes such as marked weakness, cramps, confusion or dizziness.
• Take the dose in the morning to reduce night-time urination.

Evidence & guidelines

An MHRA Drug Safety Update warns of an increased risk of non-melanoma skin cancer with cumulative hydrochlorothiazide exposure, and thiazides are recommended in NICE hypertension guidance.