A xanthine oxidase inhibitor that lowers uric acid in the blood, taken every day to prevent gout attacks and kidney stones rather than to treat an acute attack.
Legal status differs between countries and can change; each row cites the document it was taken from and applies only to the country named.
What it is used for
Preventing gout attacks by lowering blood uric acid (started after the first attack settles, especially with repeated attacks, tophi, kidney stones or kidney disease)
Preventing uric acid kidney stones
Preventing tumour lysis syndrome during chemotherapy
How it works in the body
Blocks xanthine oxidase, the enzyme that converts hypoxanthine and xanthine into uric acid at the end of purine breakdown. Blood urate falls below its saturation point, so no new crystals form and existing deposits in joints and tophi slowly dissolve over months. The dose is increased every few weeks until the urate target (below 360, or 300 micromol/L with tophi) is reached.
Common side effects
Rash (stop if it appears), nausea, diarrhoea
Gout flares in the first months
Serious: seek help
Allopurinol hypersensitivity syndrome: severe skin reactions (Stevens-Johnson, toxic epidermal necrolysis) with liver and kidney involvement, rare but life-threatening, more likely in those with the HLA-B*58:01 gene (common in Han Chinese, Thai and Korean populations, who are screened), kidney disease and high starting doses
Bone marrow suppression, liver injury (rare)
Cautions and interactions
Do not start during an acute attack; do not stop during an attack once established
Interactions: azathioprine and mercaptopurine (levels rise dangerously), warfarin, ACE inhibitors and thiazides (hypersensitivity risk)
Drink plenty of fluid; reduce dose in kidney impairment
Febuxostat is the alternative if allopurinol is not tolerated, with cardiovascular caution
Interactions
Check interactions
Taking Allopurinol with other medicines? Add them to the checker to see what the official sources say about each pair: the mechanism, general management and monitoring, never a bare "safe".
Interactions documented in the official sources cited on each card. The list covers the medicines represented on this site and is not exhaustive; how the interaction data is compiled.
Allopurinol with amoxicillin increases the chance of a skin rash.
Why it can occur
other
What official information says
UK information lists allopurinol among medicines to tell a doctor about because of the increased risk of rash.
What to discuss with a clinician
Documented; a rash during the course is reported and assessed rather than assumed to be penicillin allergy.
What may be monitored
Rash
Basis of the status
NHS: Taking amoxicillin with other medicines (tell your doctor; rash)
Sources
NHS: Amoxicillin(Taking it with other medicines and herbal supplements · Medicines that interact with amoxicillin)UK BNF: Amoxicillin interactions(Interactions)UK NHS: Allopurinol(Taking it with other medicines and herbal supplements · Medicines that interact with allopurinol)UK
Review
Facts checked against the cited sources; not yet clinically reviewed · last reviewed 12 September 2026
Medicines that share the class of Allopurinol. They are separate medicines with their own licences, doses and interactions, not alternative names for Allopurinol.
Medicines often discussed alongside Allopurinol: used together, compared with it, or acting on the same problem by a different route.
Educational content. Anatomy Nexus provides medical education and does not replace professional medical advice, diagnosis, treatment, prescribing or pharmacist review. Doses, choices and monitoring are decided by a prescriber for an individual; never start, stop or change a medicine on the basis of this page.
