Metolazon

Metolazone is a thiazide-like diuretic used to treat hypertension and edema. It acts by inhibiting the sodium-chloride (Na-Cl) cotransporter in the distal convoluted tubule of the nephron, increasing the excretion of sodium and water. Unlike classic thiazides, metolazone remains effective at lower glomerular filtration rates, and it is frequently used in combination with loop diuretics for resistant edema.

Medical uses: Metolazone is prescribed for essential hypertension and for edema associated with congestive heart failure, cirrhosis, or nephrotic syndrome. It is commonly employed when edema is not adequately controlled by a single diuretic, often in conjunction with a loop diuretic such as furosemide.

Pharmacokinetics and administration: Metolazone is taken by mouth. The diuretic effect begins within 1 to 2 hours and can persist for a day or more with a long duration of action. It is largely excreted unchanged by the kidneys. It is categorized as a thiazide-like agent, with pharmacologic effects similar to thiazide diuretics but with differences in potency and renal handling.

Adverse effects and safety: Common adverse effects include electrolyte disturbances such as hypokalemia, hyponatremia, and hypomagnesemia, along with dehydration and hyperuricemia that can precipitate gout. Photosensitivity and allergic reactions are possible. It should be used with caution in pregnancy and in patients with significant kidney impairment or electrolyte abnormalities. It may interact with other drugs; NSAIDs can reduce its diuretic effect, and concurrent use with lithium can raise lithium levels and risk toxicity. Hypotension may occur, especially with other antihypertensive agents.

History and availability: Metolazone, marketed under brand names such as Zaroxolyn, is available in tablet form in several doses. It remains a widely used agent for edema and as part of a diuretic strategy in resistant cases.