Spironolactone (marketed under the trade names Aldactone, Novo-Spiroton, Aldactazide, Spiractin, Spirotone, Verospiron or Berlactone), commonly referred to as simply spiro, is a diuretic and is used as an antiandrogen.
It is a synthetic 17-lactone drug that is a renal competitive aldosterone antagonist in a class of pharmaceuticals called potassium-sparing diuretics, used primarily to treat heart failure, ascites in patients with liver disease, low-renin hypertension, hypokalemia, secondary hyperaldosteronism (such as occurs with hepatic cirrhosis), and Conn's syndrome (primary hyperaldosteronism). On its own, spironolactone is only a weak diuretic because its effects target the distal nephron (collecting tubule), where urine volume can only be slightly modified; but it can be combined with other diuretics to increase efficacy. About one person in one hundred with hypertension has elevated levels of aldosterone; in these persons, the antihypertensive effect of spironolactone may exceed that of complex combined regimens of other antihypertensives.
Due to its antiandrogen effect, it can also be used to treat hirsutism. It is also used for treating hair loss and acne in women, and can be used as a topical medication for treatment of male baldness. It is commonly used to treat symptoms of polycystic ovary syndrome (PCOS) such as excess facial hair and acne. It can also be used as part of sex reassignment therapy by trans women.
Because spironolactone reduces the body's production of testosterone and also blocks its testosterone receptors, in men it can cause gynecomastia, impotence, erectile dysfunction, loss of sex drive and other conditions such as reduction of muscle mass, fatigue and physical weakness which are also generally associated with low testosterone levels and hypogonadism in males. For this reason, men are not typically prescribed spironolactone for any longer than a short period of time as for acute heart failure. A newer drug, eplerenone has been approved by the FDA for treatment of heart failure, has no similar anti-androgenic effects and thus is far more suitable for men for whom long term medication is contemplated. Potassium supplementation should not be administered while taking spironolactone as this may cause hyperkalemia, a potentially deadly condition. Physicians must be careful to monitor potassium levels in both males and females who are taking spironolactone, especially during the first twelve months of use and whenever dosage is increased.