Spironolactone

Aldosterone Antagonist (K⁺-Sparing Diuretic)

Drug Class: Aldosterone Antagonist (K⁺-Sparing Diuretic)
Mechanism of Action (MOA): Competitively blocks the aldosterone receptor in the collecting duct → K⁺-sparing diuresis.
Black Box Warning: Tumorigenicity — shown to be a tumorigen in chronic toxicity studies in rats; avoid unnecessary use and reserve for labeled indications.
Clinical Notes: Mortality benefit in HFrEF; also primary hyperaldosteronism and ascites. Hyperkalemia and gynecomastia (anti-androgen) — eplerenone avoids the latter.
Source: FDA label