Tiazides

Thiazide diuretics, also known as thiazides, are a class of diuretic medications that act primarily in the distal convoluted tubule of the nephron. They inhibit the sodium-chloride symporter (NCC), reducing reabsorption of sodium and chloride and increasing their excretion in urine. The resulting diuresis lowers extracellular fluid volume, and over time thiazides also reduce peripheral vascular resistance, contributing to their antihypertensive effect.

Traditional thiazides include hydrochlorothiazide and bendroflumethiazide, while thiazide-like diuretics include chlorthalidone, indapamide, and metolazone. Although all share the NCC inhibition mechanism, thiazide-like agents often have longer durations of action and may retain efficacy at lower glomerular filtration rates. Thiazides are usually taken orally, with diuretic effects beginning within hours; long-acting agents such as chlorthalidone are favored for sustained blood pressure control.

Indications for thiazides include essential hypertension and edema associated with heart failure, cirrhosis, or nephrotic syndrome. They reduce urinary calcium excretion and are sometimes used to prevent calcium-containing kidney stones. They can be employed in nephrogenic diabetes insipidus to reduce polyuria. In many guidelines, thiazides are recommended as first-line therapy for hypertension, either alone or in combination with other antihypertensives.

Common adverse effects include electrolyte disturbances such as hypokalemia and hyponatremia, plus dehydration. Hyperglycemia and hyperuricemia may occur, potentially worsening glucose tolerance or gout. NSAIDs can lessen their effectiveness and they are less reliable in significant kidney failure. They should be used with caution in pregnancy and in elderly patients, and monitoring of electrolytes is advised.