Spironolactone

Spironolactone works by blocking the mineralocorticoid receptor (also called the aldosterone receptor) in the kidneys and other tissues throughout the body ^{[1, 2]}. Aldosterone is a hormone produced by the adrenal glands that normally signals the kidneys to retain sodium and water while excreting potassium. By blocking aldosterone's effects, spironolactone causes the kidneys to excrete sodium and water (producing a diuretic effect) while retaining potassium — this is why it is classified as a "potassium-sparing" diuretic ^{[1, 3]}.

The clinical significance of this potassium-sparing property cannot be overstated. The landmark RALES trial (Randomized Aldactone Evaluation Study) demonstrated that adding low-dose spironolactone (25 mg/day) to standard heart failure therapy reduced mortality by 30% in patients with severe heart failure (NYHA class III-IV), establishing aldosterone antagonism as a cornerstone of modern heart failure management ^[3]. This benefit extends beyond simple diuresis — aldosterone contributes to cardiac fibrosis, endothelial dysfunction, and vascular inflammation, all of which spironolactone counteracts ^{[3, 7]}.

Beyond its kidney and cardiovascular effects, spironolactone also blocks androgen receptors and weakly inhibits androgen synthesis (via 17-alpha-hydroxylase inhibition) ^{[1, 4]}. These anti-androgenic properties explain its widely used off-label applications for hormonal acne and hirsutism (excess hair growth) in women. By blocking the effects of testosterone and dihydrotestosterone at the skin level, spironolactone reduces sebum production and abnormal hair growth ^{[4, 10]}.

Spironolactone is converted to several active metabolites in the body, including canrenone (half-life 16-22 hours) and 7-alpha-thiomethylspironolactone, which sustain the pharmacological effect well beyond the parent drug's short 1.4-hour half-life ^{[1, 2]}.

Week 1: The diuretic effect begins within 2-3 days of starting spironolactone. You may notice increased urination as excess sodium and fluid are eliminated ^{[1, 2]}. Unlike loop diuretics (furosemide), the onset is gradual and the diuretic effect is moderate — spironolactone is not typically used for rapid fluid removal.

Weeks 2-4: Blood pressure-lowering effects develop gradually over this period ^{[1, 3]}. For heart failure patients, symptoms of congestion (shortness of breath, swelling) may begin to improve. Your physician will check potassium levels and kidney function within the first week and then at regular intervals — hyperkalemia (elevated potassium) is the most important safety concern with this medication ^{[3, 12]}.

Months 1-3: For heart failure, the mortality benefit demonstrated in the RALES trial accrues over weeks to months of consistent therapy ^[3]. For hormonal acne or hirsutism, visible improvement typically requires 3-6 months of treatment, as the anti-androgenic effects take time to influence the hair and sebum production cycles ^{[4, 10]}. Patience is essential — dermatologic benefits are not immediate.

Hormonal side effects: You may notice breast tenderness or enlargement (gynecomastia in men, breast tenderness in women), which occurs in approximately 10% of patients and is related to the anti-androgenic and progestational effects ^{[1, 3]}. Women may experience menstrual irregularities, including spotting or amenorrhea ^{[1, 4]}. These effects are dose-dependent and may improve with dose reduction.

Ongoing monitoring: Long-term use requires periodic monitoring of potassium, creatinine, and blood pressure ^{[1, 7, 12]}. The risk of hyperkalemia is highest in patients with renal impairment, those taking ACE inhibitors or ARBs, and elderly patients.

Spironolactone should be taken with food, which increases absorption by approximately 100% and is generally recommended for optimal bioavailability ^{[1, 2, 9]}. Taking it with a meal also reduces the likelihood of gastrointestinal side effects.

Potassium-rich foods: While you do not need to eliminate potassium-rich foods from your diet, you should avoid dramatically increasing your intake of high-potassium items such as bananas, oranges, potatoes, tomatoes, avocados, and especially salt substitutes (which contain potassium chloride and can cause dangerous potassium elevation) ^{[1, 7, 12]}. Discuss your dietary potassium intake with your doctor, particularly if you are also taking an ACE inhibitor or ARB.

Alcohol: Alcohol may enhance the blood pressure-lowering effect of spironolactone, causing dizziness or lightheadedness, especially when standing up quickly (orthostatic hypotension) ^{[1, 2]}. Moderate consumption is generally acceptable for most patients. However, for patients taking spironolactone for liver cirrhosis with ascites, alcohol must be completely avoided as it directly worsens the underlying liver disease ^[11].

Natural licorice (glycyrrhizin): Avoid natural licorice root products, which contain glycyrrhizin — a compound that has aldosterone-like effects ^{[1, 9]}. Glycyrrhizin promotes sodium and water retention while increasing potassium excretion, directly counteracting spironolactone's therapeutic mechanism. Note that most American licorice candy is flavored with anise, not real licorice, and does not contain glycyrrhizin.

Heart failure (NYHA class III-IV) [1, 3, 7]: - Starting: 25 mg once daily (12.5 mg if serum potassium >5.0 mEq/L or eGFR is borderline) - Target: 25-50 mg once daily - Check potassium at 1 week, then at 1 month, then every 3 months - Hold or reduce dose if potassium rises above 5.5 mEq/L

Hypertension [1, 2]: - Starting: 25-50 mg daily in 1-2 divided doses - Maximum: 100 mg/day (some resistant hypertension guidelines support up to 200 mg) - Particularly effective as add-on therapy for resistant hypertension

Edema from hepatic cirrhosis [1, 11]: - Starting: 100 mg daily (often combined with furosemide in a 100:40 mg ratio to maintain potassium balance) - Maximum: 400 mg/day - The spironolactone-to-furosemide ratio helps prevent both hypokalemia and hyperkalemia

Acne and hirsutism (off-label) [4, 10]: - Starting: 25-50 mg daily - Maintenance: 50-200 mg daily - Allow 3-6 months for full dermatologic effect - Lower doses (50-100 mg) are often sufficient for acne

Available strengths: 25 mg, 50 mg, 100 mg tablets ^{[1, 2]}. CaroSpir oral suspension (25 mg/5 mL) is available for patients unable to swallow tablets.

Generic spironolactone is widely available and affordable, making cost rarely a barrier to treatment ^{[1, 8]}.

Generic spironolactone tablets: Approximately $5-20 per month for most commonly prescribed doses (25-100 mg) ^[8]. Available on most $4 generic medication lists at major pharmacy chains. A 90-day supply is often $10-15.

Brand Aldactone: Largely discontinued in favor of generics. When available, it costs significantly more with no clinical advantage ^{[1, 5]}.

CaroSpir (brand oral suspension): Substantially more expensive — approximately $200-400 per month. Use generic tablets when the patient can swallow them. For patients requiring a liquid formulation, compounding pharmacies can prepare spironolactone suspension at a fraction of the CaroSpir price.

Insurance coverage: Most insurance plans cover generic spironolactone at the lowest copay tier ^[8]. GoodRx coupons can further reduce out-of-pocket costs to as low as $4-8 for a 30-day supply.

Compared to eplerenone: Eplerenone (Inspra) is a more selective mineralocorticoid receptor antagonist with fewer anti-androgenic side effects, but it is significantly more expensive — $100-300+ per month even as a generic ^[8]. For most indications, spironolactone is the first-choice agent based on cost-effectiveness.

Spironolactone is CONTRAINDICATED in pregnancy ^{[1, 2, 6]}. It crosses the placenta and its anti-androgenic effects pose a serious risk to male fetuses. Animal studies and case reports have documented feminization of male fetuses (ambiguous genitalia) when exposed to spironolactone or similar anti-androgens during critical periods of sexual differentiation ^{[1, 6]}.

Women of childbearing potential should use effective contraception while taking spironolactone ^{[1, 4]}. For women using spironolactone for acne or hirsutism, many dermatologists recommend concurrent oral contraceptive use, which provides both contraception and complementary anti-androgenic effects ^{[4, 10]}. Pregnancy testing may be recommended before initiating therapy.

If pregnancy occurs while taking spironolactone, the medication should be discontinued immediately and the patient should consult their obstetrician. The risk of fetal harm is greatest during the first trimester when genital differentiation occurs, but exposure at any gestational age is concerning ^{[1, 6]}.

Breastfeeding: Canrenone, the primary active metabolite of spironolactone, is excreted in breast milk ^{[1, 2]}. The WHO considers spironolactone compatible with breastfeeding at doses up to 200 mg/day, based on estimated infant exposure levels. However, some clinical references recommend caution, particularly at higher doses. Monitor the infant for any adverse effects including poor feeding, lethargy, or GI disturbance ^[9]. If an aldosterone antagonist is needed during lactation, discuss the risks and benefits with both the prescriber and pediatrician.

Generic spironolactone has been available for decades and is the universal standard of care ^{[1, 2, 5]}. All generic spironolactone tablets are FDA-rated AB (therapeutically equivalent) to brand Aldactone, meaning they have demonstrated identical bioavailability in controlled pharmacokinetic studies ^[5].

There is no clinical reason to use brand-name Aldactone over generic spironolactone ^{[1, 5, 8]}. The active ingredient, dosing, and therapeutic outcomes are identical. Generic spironolactone is available from multiple manufacturers in 25 mg, 50 mg, and 100 mg tablet strengths.

CaroSpir is a branded oral suspension (25 mg/5 mL) designed for patients who cannot swallow tablets — including elderly patients with dysphagia and pediatric patients ^[2]. It is significantly more expensive than generic tablets. For patients needing a liquid formulation, a compounding pharmacy can prepare spironolactone oral suspension from crushed tablets at substantially lower cost.

Eplerenone (Inspra) is an alternative MR antagonist with greater selectivity for the mineralocorticoid receptor and fewer anti-androgenic side effects (less gynecomastia, no menstrual irregularity) ^[7]. However, eplerenone is considerably more expensive and is typically reserved for patients who cannot tolerate spironolactone's hormonal side effects.