Thiazid

Thiazid, commonly spelled thiazide in medical literature, refers to a class of diuretic medications that act on the distal convoluted tubule of the kidney. They inhibit the sodium-chloride co-transporter (NCC) in the luminal membrane, reducing reabsorption of sodium and chloride. The resulting diuresis lowers extracellular fluid volume and, with time, decreases blood pressure. Thiazides also promote calcium reabsorption in the distal nephron, contributing to a lower urinary calcium excretion.

Prototypical members include hydrochlorothiazide and chlorthalidone. Other commonly used thiazides and thiazide-like agents include bendroflumethiazide, bendrofluazide, indapamide, and metolazone. While indapamide and metolone are sometimes described as thiazide-like due to differences in structure or pharmacokinetics, they share the same general mechanism of NCC inhibition and diuretic effect.

Uses and indications: Thiazides are widely used as first-line or second-line therapy for essential hypertension and are effective in reducing cardiovascular events. They are also employed to treat edema associated with heart failure, cirrhosis, and nephrotic syndrome. In some patients, thiazides reduce urinary calcium loss and help prevent calcium-containing kidney stones. They may be used in nephrogenic diabetes insipidus to decrease polyuria.

Pharmacokinetics: Onset of action occurs within 1–2 hours for some agents, with peak effects after several hours. The duration varies: shorter-acting thiazides provide relief for about 6–12 hours, while some agents (notably chlorthalidone) have longer durations of action.

Adverse effects and interactions: Common risks include hypokalemia, hyponatremia, dehydration, and hyperuricemia (gout). Hyperglycemia or impaired glucose tolerance can occur, particularly in susceptible individuals. Photosensitivity is possible. NSAIDs can diminish diuretic efficacy; lithium carries a risk of toxicity when combined with thiazides. Monitoring of electrolytes, uric acid, and glucose is advised during therapy.