Spironolactone
Spironolactone blocks sodium reabsorption, by antagonism of aldosterone. Low-dose spironolactone (25 mg daily) in combination with a loop diuretic and an angiotensin converting enzyme (ACE) inhibitor has been shown to improve prognosis in patients with severe heart failure.
Spironolactone is also a relatively weak antiandrogen and is used to treat visible manifestations of androgenisation in women (eg acne, androgenetic alopecia and hirsutism). It acts by competitive binding and blockade of the androgen receptor. It may be used for treatment of hirsute women in whom blood testosterone levels are low.
Hyperkalaemia may occur if spironolactone is used in combination with potassium supplements, ACE inhibitors, potassium-sparing diuretics or angiotensin II receptor blockers—particularly in patients with renal impairment. Before initiating therapy with spironolactone, monitor baseline potassium, and then review at 1 week, 1 month, and thereafter every 3 months, or if adjusting the dose or there are changes in renal function.
The active metabolite of spironolactone is an antagonist of aldosterone and of androgens. The latter property leads to gynaecomastia in men and intermenstrual or postmenopausal bleeding in women. Spironolactone is often used with a combined oral contraceptive in women to improve its antiandrogenic effectiveness and to avoid the relatively common adverse effect of irregular menstruation. Other adverse effects associated with spironolactone include tender and enlarged breasts, polyuria (with initial therapy), postural hypotension and loss of sodium.
Antiandrogens are teratogenic and have the potential to feminise male fetuses. They should be avoided in pregnancy; contraception is imperative in women of child-bearing potential who are using antiandrogens.
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