Drug Mnemonic

Spironolactone

Aldosterone antagonist • K⁺-sparing diuretic • antiandrogen
June 1, 2026

A story built from the name spironolactone itself - so the mechanism of action, key side effects, and the way Step 1 actually tests it stick on the first read.

RxMnemonic Diuretics
Spironolactone
Aldosterone antagonist • K⁺-sparing diuretic • antiandrogen
SPIRONO = spy on aldo + LACTONE = lactate
Separate spironolactone into SPIRONO (sounds like spy on Aldo) and LACTONE (sounds like lactate). Imagine a spy on Aldo, tailing him and blocking everything he does. Aldo is taping holes in the barrel to keep water in, and the spy keeps ripping the tape off to let the water out. Lactone sounds like lactate, your reminder for the classic side effects: lactation and gynecomastia.
Spironolactone pharmacology mnemonic illustration
Diuretics SPIRONO = spy on Aldo | LACTONE = lactate
HOW STEP TESTS IT
1
Spironolactone blocks the aldosterone receptor in the collecting duct, so you keep potassium while excreting sodium and water. The most dangerous side effect is hyperkalemia, which worsens with ACEi or ARBs.
2
It blocks androgen receptors, causing gynecomastia and menstrual irregularities, which is what makes spironolactone useful in treating PCOS and hirsutism. It lowers heart failure mortality and is first-line for cirrhotic ascites. 
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Practice Question

A 71-year-old woman with HFrEF and an eGFR of 38 is on lisinopril and metoprolol. Spironolactone is added. Two weeks later, she presents with fatigue and a wide-complex bradycardia. The most likely contributor is:

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Pharmacology Summary

Spironolactone: Mechanism, Uses & High-Yield Facts for USMLE Step 1

Spironolactone is a competitive aldosterone receptor antagonist that blocks sodium reabsorption and potassium excretion in the collecting duct, making it a potassium-sparing diuretic. The primary risk is hyperkalemia, which becomes especially dangerous when combined with ACE inhibitors or ARBs in patients with reduced GFR. It also blocks androgen receptors, causing gynecomastia and menstrual irregularities — useful clinically for PCOS and hirsutism. Spironolactone reduces mortality in heart failure with reduced ejection fraction and is first-line for managing cirrhotic ascites.

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