Allopurinol
A xanthine oxidase inhibitor taken long term to prevent gout attacks, some kidney stones and high uric acid during cancer treatment.
Drug card
- How it works
- Blocking xanthine oxidase so the body makes less uric acid
- Used for
- Chronic gout, to prevent attacks and tophi
- High uric acid from cancer treatment (tumor lysis)
- Recurrent calcium oxalate kidney stones
- Known for
- Rash, its most frequent side effect
- Severe skin reactions (SJS, TEN, DRESS)
Study it as a flashcard, and it comes back before you forget it.
Mechanism of action
How does allopurinol work?
Allopurinol is a structural analogue of hypoxanthine. It and its metabolite oxypurinol inhibit xanthine oxidase, so less uric acid is made, without disturbing purine synthesis. Unlike uricosuric drugs, it lowers uric acid in urine as well as blood.
Like other xanthine oxidase inhibitors: Xanthine oxidase turns hypoxanthine into xanthine and xanthine into uric acid, the last step of purine breakdown in humans. Blocking it lowers uric acid in blood and urine, so over months the body's urate stores shrink and gout attacks become rarer. The same block slows the breakdown of azathioprine and mercaptopurine, raising their levels.
Uses
What is allopurinol used for?
- Chronic gout, to prevent attacks and tophi
- High uric acid from cancer treatment (tumor lysis)
- Recurrent calcium oxalate kidney stones
Side effects
Side effects of allopurinol
- Rash, its most frequent side effectKnown for
- Severe skin reactions (SJS, TEN, DRESS)Known forSerious
- Gout flares when treatment starts
- Nausea and vomiting
- Diarrhea
- Drowsiness and dizziness
- Liver injury and raised liver enzymesSerious
- Worsening kidney functionSerious
- Bone marrow suppressionSerious
- Severe allergic reactions (anaphylaxis)Serious
Known for marks what an exam expects you to know it for.
Watch for
Cautions and what sets it apart
- HLA-B*58:01 carriers, more common in Han Chinese, Korean, Thai and African ancestry, risk severe skin reactions; consider testing first.
- Stop at the first rash; ampicillin, amoxicillin, thiazides and bendamustine raise the risk of severe rash.
- It raises azathioprine and mercaptopurine levels, so their doses must be cut sharply.
- Lower doses are needed when kidney function is reduced.
Good to know: The usual first urate-lowering drug: febuxostat is kept for people who do not respond to allopurinol or cannot take it.
Remember it
A way to remember it
Xanthine oxidase inhibitors shut the uric acid factory; they don't open the drain.
They lower uric acid by cutting its production, unlike uricosuric drugs, which raise its loss in urine. As stores shrink, urate moves out of tissues, which is why flares rise at first.
Written for biofideX
Its class
Xanthine oxidase inhibitors
Other xanthine oxidase inhibitors with a card:
Easily mixed up with colchicine and non-steroidal anti-inflammatory drugs.
Sources
Checked against
Written for biofideX in plain words, after checking these references:
- Allopurinol tablets: label (DailyMed)
- Allopurinol (NCI Thesaurus)
- Allopurinol (NHS)
- Febuxostat tablets: label (DailyMed)
For learning pharmacology, not for treatment decisions: no doses are given, and a prescriber, pharmacist or the product's own label is the word on any one patient. Spotted a mistake? Tell us and we'll correct it.
Pain, fever and inflammation
Allopurinol is one of 15 drugs practiced together here: their classes, how they work, what they treat and what they're known for.
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