Drug Mnemonic

Allopurinol

AntiGout • Xanthine oxidase Inhibitor • gout prevention
May 4, 2026

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

RxMnemonic Antigout
Allopurinol
AntiGout • Xanthine oxidase Inhibitor • gout prevention
ALLO = all + PURIN = purines +OL = all
Separate allopurinol into ALLO (sounds like All), PURIN (sounds like purine), and OL (sounds like all again). Allopurinol is ALL - PURINE - ALL. It loves purines so much that it blocks ALL other love (XO) from both sides, thus ALL - PURINE - ALL. And XO? That stands for the enzyme allopurinol blocks: Xanthine Oxidase (XO). 
Allopurinol pharmacology mnemonic illustration
Antigout ALLO = all | PURIN - purine | OL = all
HOW STEP TESTS IT
1
Allopurinol inhibits xanthine oxidase, blocking hypoxanthine -> xanthine -> uric acid, lowering serum urate and preventing gout flares.
2
Side effects: Can paradoxically trigger a gout flare on initiation. Avoid in patients taking azathioprine or 6-mercaptopurine (xanthine oxidase metabolizes both and blocking xanthine oxidase causes these to accumulate at toxic levels. 
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Practice Question

A 52 year-old man with chronic gout is started on allopurinol. Three weeks later he returns with a swollen, hot first MTP joint. What is the most appropriate step?

More Antigout

Colchicine
← AliskirenDigoxin →
Pharmacology Summary

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

Allopurinol inhibits xanthine oxidase, blocking the conversion of hypoxanthine to xanthine to uric acid and lowering serum urate. It is used for chronic gout prevention and hyperuricemia from tumor lysis syndrome. Starting it can paradoxically trigger a gout flare from urate crystal mobilization, so colchicine prophylaxis is often added at initiation. A high-yield drug interaction: avoid combining allopurinol with azathioprine or 6-mercaptopurine, because xanthine oxidase metabolizes both and blocking it causes toxic accumulation.

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