Spironolattone

Spironolactone is a potassium-sparing diuretic and a mineralocorticoid receptor antagonist. It blocks the action of aldosterone in the distal nephron, reducing sodium reabsorption and increasing potassium retention. It also has antiandrogenic effects, partly by inhibiting androgen receptors and, at higher doses, decreasing androgen synthesis.

Commonly used for edema associated with heart failure, cirrhosis, or nephrotic syndrome; for hypertension, especially where resistant or hypokalemia risk is a concern; and as part of therapy for primary hyperaldosteronism. It is also used off-label for acne and hirsutism in women due to its antiandrogen properties. In heart failure, spironolactone reduces morbidity and mortality when added to standard therapy.

Administration and pharmacokinetics: spironolactone is taken orally. It is metabolized in the liver to active metabolites, such as canrenone, contributing to its diuretic and antiandrogen effects. The onset of diuretic action typically occurs within 24 hours, with peak effects over several days. The drug is excreted in urine and bile.

Safety and adverse effects: a major concern is hyperkalemia, especially in patients with renal impairment, diabetes, or concurrent use of ACE inhibitors, ARBs, or potassium supplements. Other adverse effects include dizziness, gastrointestinal upset, fatigue, gynecomastia, breast tenderness, menstrual irregularities, and, less commonly, rash. Spironolactone is generally avoided in pregnancy due to potential effects on fetal development and is used with caution during lactation.

Contraindications and interactions: contraindicated in hyperkalemia, significant renal impairment, and anuria. It can interact with other potassium-sparing agents and with drugs that raise potassium levels or affect renal function.