Spironolactone vs Eplerenone for Primary Aldosteronism?

Both spironolactone and eplerenone treat primary aldosteronism by blocking the effects of excess aldosterone in your body ^[1]. When primary aldosteronism affects both adrenal glands (bilateral disease), or when surgery is not an option for unilateral disease, medical therapy with one of these drugs is often the standard of care.

Spironolactone is generally the first-line medical therapy when a medication in this class is indicated. It is highly effective, widely available, and usually less expensive ^[1]. However, it can cause side effects related to sex hormones, such as breast tenderness or menstrual irregularities. Eplerenone is a more selective alternative that is much less likely to cause these side effects ^[2]. Eplerenone can be more expensive and may require twice-daily dosing ^[1].

Warning: Spironolactone and eplerenone are not milligram-for-milligram interchangeable. Never start, stop, or adjust your dose without your clinician’s guidance.

How They Work

Both medications belong to a class of drugs called mineralocorticoid receptor antagonists (MRAs). They work by preventing aldosterone from binding to its receptors. This helps lower your blood pressure and reduces your body’s excretion of potassium, bringing low potassium levels back toward normal ^[3][4].

When dosed appropriately, both medications are effective ^[1]. Spironolactone is generally more potent. Some research suggests it may be slightly better at lowering blood pressure and correcting low potassium, though differences are small ^[2][5]. Because eplerenone is less potent, you may need a higher dose or a twice-daily schedule to achieve the same results ^[6].

Monitoring Renin

Your doctor will likely monitor a blood test called renin to see if the medication is working. Excess aldosterone suppresses renin, so a rise in your renin levels is a useful biomarker that the medication is adequately blocking the excess aldosterone ^[1][7]. There is no single universal “target” number; your doctor will interpret your renin based on the specific lab assay used, alongside your blood pressure, potassium, and overall clinical picture.

Side Effect Differences

A key difference between the two medications is their side effect profile, specifically regarding sex hormones.

Spironolactone Side Effects

Spironolactone effectively blocks the aldosterone receptor, but it also binds to androgen receptors (which respond to hormones like testosterone) and stimulates progesterone receptors ^[3][1]. This can lead to anti-androgen side effects:

• Breast tenderness or gynecomastia (breast enlargement) in men ^[2]
• Menstrual irregularities in women ^[8]
• Reduced libido or sexual dysfunction ^[8]

These side effects can occur at any dose, though the risk generally increases at higher doses and with longer-term use ^[9].

Eplerenone Side Effects

Eplerenone was designed to be more selective, meaning it primarily targets the aldosterone receptor without interfering as much with sex hormones ^[3][10]. As a result, it is much less likely to cause gynecomastia or menstrual changes, though sexual symptoms are still possible ^[11][2]. It is often prescribed as an alternative if a patient experiences bothersome side effects from spironolactone ^[12].

Shared Risks: Potassium, Kidneys, and Drug Interactions

Because both medications work the same way, they share important risks.

High Potassium (Hyperkalemia)

While these drugs correct low potassium, they can also cause your body to hold onto too much potassium, raising it to dangerously high levels ^[13]. This risk is higher if you have kidney disease or are older ^[14]. High potassium often causes no symptoms, but severe cases can lead to severe weakness, palpitations, or fainting—seek urgent medical help if these occur.

You must review all your medications and supplements with your doctor before starting or changing your dose. The risk of high potassium increases significantly if you take:

• Potassium supplements or potassium-containing salt substitutes (these are often stopped once MRA treatment begins) ^[4]
• Blood pressure medications like ACE inhibitors or ARBs ^[14]
• NSAID pain relievers (like ibuprofen)
• Certain antibiotics (like trimethoprim)

Eplerenone also has important interactions with drugs that affect the CYP3A4 liver enzyme, which can change how it is processed in the body. Check with your pharmacist before starting any new prescription or over-the-counter medicine.

Kidney Function Changes

Your kidney function is measured by a blood test called eGFR (estimated glomerular filtration rate). When you start treatment, your eGFR may decline ^[15]. Excess aldosterone forces the kidneys to filter too quickly (a process called hyperfiltration). MRAs lower the pressure inside the kidneys, returning filtration to a more normal rate, which causes the eGFR number to drop ^[16][17].

While a modest drop can be an expected hemodynamic change rather than actual kidney damage ^[18], any significant, rapid, or progressive change requires prompt clinical review to ensure your blood pressure hasn’t dropped too low or that there is no underlying kidney injury ^[19].

Monitoring Plan

Your doctor should order baseline blood tests to check your potassium and eGFR before you start. These should be rechecked shortly after starting the medication and after any dose change, with ongoing follow-up based on your individual risk factors ^[14]. Other common side effects to watch for include dizziness, low blood pressure, and increased urination.

Comparison Summary