Triamterene with chlortalidone

How it works

Chlortalidone inhibits the distal tubular sodium-chloride co-transporter to produce sustained natriuresis, while triamterene blocks distal epithelial sodium channels to reduce potassium excretion, balancing the potassium-losing effect of the thiazide-like component.

Prescribing in practice

• The triamterene component risks hyperkalaemia, which is amplified by renal impairment and by concomitant ACE inhibitors, ARBs, potassium supplements or potassium-sparing agents, so these combinations need care.
• Chlortalidone has a long duration of action and can cause hypokalaemia, hyponatraemia, hyperuricaemia and impaired glucose tolerance, so the two components are balanced but still require electrolyte vigilance.
• It is contraindicated in significant renal impairment, anuria and pre-existing hyperkalaemia.

Monitoring

Monitor serum potassium, sodium and renal function before starting and periodically thereafter, especially in older patients or those on interacting drugs.

Counselling the patient

• Avoid potassium-containing salt substitutes unless advised.
• Report muscle weakness, palpitations, cramps or confusion.
• Keep up with the blood tests for your kidneys and potassium.

Evidence & guidelines

Combining a potassium-sparing diuretic with a thiazide-like agent to offset potassium loss is a long-established approach, and chlortalidone has robust outcome data for blood-pressure lowering in hypertension.