Spironolactone

Spironolactone (marketed under the trade names Aldactone, Novo-Spiroton, Spiractin, Spirotone, Verospiron or Berlactone) is a diuretic and is used as an antiandrogen.

It is a synthetic 17-lactone drug which 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, and Conn's syndrome as well as high blood pressure. On its own, spironolactone is only a weak diuretic, but it can be combined with other diuretics. 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 anti-androgen effect, it can also be used to treat hirsutism, and is a common component in hormone therapy for male-to-female transsexual and transgendered people. 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.

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Mechanism of action

Spironolactone inhibits the effect of aldosterone by competing for intracellular aldosterone receptor in the distal tubule cells (it actually works on Aldosterone receptors in the collecting duct). This increases the secretion of water and sodium, while decreasing the excretion of potassium. Spironolactone has a fairly slow onset of action, taking several days to develop and similarly the effect diminishes slowly. Spironolactone has anti-androgen activity by binding to the androgen receptor and thus preventing it to interact with dihydrotestosterone.^[1]

Pharmacokinetics

Spironolactone is fairly rapidly absorbed from the gastrointestinal tract. It is also rapidly metabolised and bound in plasma proteins. Many of its metabolites are also active and one of them, canrenone as potassium canrenoate, is used parenterally when rapid effect is needed. Spironolactone's half-life is 85 minutes, but canrenone's half-life is 10 to 35 hours, depending on the dose. The main elimination route is in the urine and some also in the bile.

Mortality and morbidity benefit in severe heart failure

Spironolactone was shown to have a significant mortality and morbidity benefit in the Randomized Aldactone Evaluation Study (RALES), which studied people with severe congestive heart failure (New York Heart Association functional class III or IV).^[2] Patients in the study arm of the trial (those receiving spironolactone) had a relative risk of death (when compared to the placebo group) equal to 0.70 or a 30% relative risk reduction. Patients in the study arm also had significantly less symptoms of CHF and were hospitalized less frequently.

The mechanism of this effect is also mediated by inhibiting aldosterone, which in heart failure leads to myocardial fibrosis, sodium retention, and vascular dysfunction.

Adverse effects and interactions

Spironolactone is associated with an increased risk of bleeding from the stomach and duodenum, but a causal relationship between the two has not been established.^[3] Since it also affects steroid receptors elsewhere in the body, it can cause gynecomastia, menstrual irregularities and testicular atrophy. Other side effects include ataxia, erectile dysfunction, drowsiness and rashes. A carcinogenic effect has been demonstrated in rats. Spironolactone has been shown to be immunosuppressive in the treatment of sarcoidosis.^[4]

People using this drug should avoid salt substitutes containing potassium.^[5]

Carcinogenicity

Studies of spironolactone and the related compound potassium canrenoate (which, like spironolactone, metabolizes to canrenone) in rats for one to two year periods show an increase in carcinogenesis in the thyroid gland, testes, liver, breasts, and myelocytic leukocytes. Mammalian cells, depending on the presence of metabolic activation, show mixed results for mutagenicity in vitro.^[6] In light of this research, Sandoz has recommended that unnecessary use of spironolactone be avoided.

See also

• Baldness treatments

References