Gout agents · Pain & inflammation
Allopurinol
Zyloprim®(brand names vary by market)
Lowers urate over months, and does nothing for the attack in front of you.
Mechanism
Xanthine oxidase inhibitor: less conversion of hypoxanthine and xanthine to uric acid, so serum urate falls and crystal stores dissolve over months.
Indications
- Gout, urate lowering
- Tumour lysis syndrome prophylaxis
- Recurrent uric acid stones
Formulations
Dosing concepts
Start low, go slow
Started at a low dose and titrated upward against serum urate, both to reduce hypersensitivity risk and to avoid provoking flares.
Flare prophylaxis
Anti-inflammatory cover, usually colchicine, runs alongside for the first months, because falling urate mobilises crystals and precipitates attacks.
Continue through a flare
It is not started during an acute attack, but an existing prescription is never stopped during one.
Concepts, not prescribing instructions. Practice numbers live in current references and local protocols.
Pharmacokinetics
- Bioavailability
- ~80%
- Half-life
- Allopurinol 1 to 2 h; the active metabolite oxypurinol 15 to 30 h
- Elimination
- renal: Oxypurinol is renally cleared and accumulates in impairment
- Protein binding
- Negligible
Adverse effects
- Rashcommon & seriousStopped at the first sign, because the severe reactions begin as an ordinary-looking rash.
- Allopurinol hypersensitivity syndromeseriousRash, fever, eosinophilia, hepatitis and renal failure. Mortality is substantial and HLA-B*5801 carries much of the risk.
- Precipitation of gout flares on startingcommon
- Transaminase elevationcommon
Contraindications & precautions
Contraindications
- Prior allopurinol hypersensitivity
Precautions
- Renal impairment
- HLA-B*5801-positive ancestry groups
- Concurrent azathioprine or mercaptopurine, whose metabolism it blocks
Interactions
No curated interaction entries yet for this agent.
Monitoring
Serum urate against a target
The dose is titrated against it, not against symptoms · Every few weeks during titration, then periodically
Rash, at any point
The severe reactions announce themselves this way
Renal and hepatic function
Dose and toxicity
Counselling points
- This prevents future attacks; it will not help the one you have now.
- You may get more attacks in the first months. That is expected, and it is why you also have an anti-inflammatory.
- Stop it and contact us immediately if you develop a rash.
- Keep taking it during an attack once you are established on it.
- Drink plenty of fluids.
Clinical pearls
- Stopping allopurinol during a flare is a very common mistake that prolongs the whole problem; the fluctuation in urate is itself a trigger.
- With azathioprine or mercaptopurine it blocks the main route of inactivation and can cause profound marrow suppression. The combination requires a large dose reduction or a different urate-lowering drug.
References & review
- Allopurinol product monograph (consult the current version for your market) (monograph)
- Goodman & Gilman's The Pharmacological Basis of Therapeutics, 14th ed. (reference-work)
Last reviewed 2026-08-16 · jurisdiction: global · drug information changes; verify against current references before practice use.