Pharmacotherapy Newsletter

Volume 2, Issue 13, 03/30/2010

Question

How does the aldosterone antagonist, eplerenone (Inspra) cause less gynecomastia than spironolactone (Aldactone)?

Answer

The two aldosterone antagonists on the market that are commonly used for the treatment of hypertension (HTN) and/or heart failure (HF) due to left ventricular systolic dysfunction are eplerenone (Inspra) and spironolactone (Aldactone).(1,2)  In addition to these indications, spironolactone is available generically, is less prone to drug interactions and is also used in the management of primary aldosteronism, edema from cirrhosis, and prophylaxis against hypokalemia.(2)  However, spironolactone is known to cause more gynecomastia and/or breast pain in male patients than eplerenone.  For example, the RALES trial revealed that spironolactone caused gynecomastia and breast pain in 10% of HF patients whereas only 0.5% of HF patients on eplerenone in the EPHESUS trial.(3,4)  This low incidence of gynecomastia with eplerenone is also consistent in patients with HTN where it was not different from placebo.(1) 

What regulates breast tissue proliferation in males that normally prevents the formation of gynecomastia?
In short, there is a balance between the inhibition of...

The complete answer to this question comes with a diagram that explains the mechanism for this difference in side effect.

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