Spironolactone
Spironolactone is a potassium-sparing diuretic that blocks the aldosterone receptor. It is used in heart failure, resistant hypertension, ascites and androgen-related conditions in women, and is on the WHO Essential Medicines List.
- Chemical formula
- C24H32O4S
- CAS number
- 52-01-7
- ATC code
- C03DA01
- Molecular weight
- 416.57 g/mol
- Drug class
- Potassium-sparing diuretic / aldosterone antagonist
- Also known as
- Aldactone, Spirolactone
What is it?
Spironolactone is an aldosterone receptor antagonist used since the 1960s, primarily marketed as Aldactone. It is on the WHO Essential Medicines List and is widely available as authorised generic. The molecule is mainly used in cardiovascular and hepatic medicine but also has well-established off-label uses in dermatology and gynaecology because of its anti-androgen activity.
Mechanism of action
Spironolactone competitively blocks the mineralocorticoid (aldosterone) receptor in the distal tubule of the kidney, reducing sodium reabsorption and potassium excretion. It also has weak androgen-receptor antagonism and mild progestogen effects, which underlie its dermatological and gynaecological uses. The diuretic effect develops over days as aldosterone-mediated sodium retention is unwound.
Pharmacokinetics
Spironolactone is well absorbed after oral administration, especially with food. It undergoes extensive hepatic metabolism to several active metabolites, including canrenone and 7α-thiomethylspirolactone, which contribute to most of its clinical effect. The half-life of spironolactone itself is short (~1–2 hours), but the active metabolites have half-lives of 13–24 hours, supporting once or twice daily dosing.
Indications
Spironolactone is approved for heart failure with reduced ejection fraction, primary hyperaldosteronism, resistant hypertension, oedema in cirrhosis or nephrotic syndrome, and certain potassium-loss states. Off-label uses include female pattern hair loss, hirsutism, polycystic ovary syndrome and acne in women, where the anti-androgen effect is therapeutic.
Safety profile
Common adverse effects include hyperkalaemia (especially with renal impairment or ACE inhibitors), gynaecomastia in men, menstrual irregularities in women, and dizziness from blood pressure effects. Serum potassium and renal function require monitoring during initiation and dose titration. Spironolactone is contraindicated in severe hyperkalaemia, severe renal impairment and Addison disease.
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Frequently asked questions
Why is spironolactone used for acne and hair loss in women? ▾
Spironolactone has anti-androgen activity that reduces the action of testosterone and DHT on skin and hair follicles. In women with acne or female pattern hair loss with hormonal contributors, doses of 50–200mg daily can improve symptoms over months. According to dermatology guidelines, it is used off-label in adult women only and is contraindicated in pregnancy.
How does spironolactone differ from other diuretics? ▾
Most diuretics (loops, thiazides) waste potassium; spironolactone retains it. This makes it useful as a potassium-sparing combination partner for loops and thiazides, and as monotherapy in conditions where aldosterone excess drives the problem (heart failure, primary aldosteronism). It is less powerful as a pure diuretic than furosemide.
What lab tests are needed on spironolactone? ▾
Serum potassium and creatinine are checked at baseline, within 1–2 weeks of starting or dose increase, and periodically thereafter. According to the prescribing information, hyperkalaemia is the main risk and is amplified by ACE inhibitors, ARBs, NSAIDs and renal impairment.
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