thiazide diuretic
A thiazide diuretic is the gentle, steady workhorse of blood pressure treatment. Rather than flushing out fluid in a sudden rush, it nudges the kidney to let go of a modest amount of salt and water continuously, like leaving a tap dripping rather than throwing the bucket out. This slow offloading suits long-term control of mild hypertension.
Thiazides act on the distal convoluted tubule of the kidney, where they block the sodium-chloride cotransporter. Less sodium is reabsorbed, so more sodium and water leave in the urine. Over weeks, beyond the volume effect, the arteries themselves relax, giving an additional pressure-lowering action. Examples include hydrochlorothiazide, bendroflumethiazide and the thiazide-like agents indapamide and chlortalidone.
They are inexpensive, effective first-line antihypertensives, but they reliably lower potassium and can lower sodium, raise blood sugar, raise uric acid (triggering gout) and raise calcium. Their diuretic effect fades when kidney function is poor, so loop diuretics are preferred in significant renal impairment. Electrolytes are monitored, particularly in older patients prone to low sodium.
An older patient with stage 1 hypertension and normal kidneys starts low-dose indapamide, a thiazide-like diuretic, achieving smooth blood pressure control with one inexpensive daily tablet.
Low-dose thiazides give most of the benefit with fewer metabolic side effects than high doses.
A neat contrast: thiazides retain calcium while raising it slightly, whereas loop diuretics flush calcium out, which is why each is chosen for different stone and bone situations.