Hydrochlorothiazide

How it works

It inhibits the sodium-chloride cotransporter in the distal convoluted tubule, increasing sodium and water loss while paradoxically enhancing distal calcium reabsorption, which lowers urinary calcium.

Prescribing in practice

• It can cause clinically important electrolyte disturbance, notably hyponatraemia and hypokalaemia, so check electrolytes before starting and during treatment, particularly in the elderly.
• Thiazides raise serum urate and can precipitate gout, and may unmask or worsen glucose intolerance.
• Efficacy as a diuretic falls in significant renal impairment, where a loop diuretic is usually preferred.

Monitoring

Monitor urea and electrolytes (especially sodium and potassium), renal function, and where relevant urate and glucose.

Counselling the patient

• Take in the morning to avoid night-time passing of urine.
• Report persistent dizziness, muscle cramps, marked thirst or confusion, which may indicate salt imbalance.

Evidence & guidelines

Thiazide and thiazide-like diuretics are well established for hypertension and, per stone-prevention guidance, reduce recurrence in hypercalciuric calcium stone formers.