Allopurinol
Pronunciation: pronunciation varies by local usage.
- Generic name
- allopurinol
- Brand names
- Zyloprim, Zyloric
- Drug class
- Xanthine oxidase inhibitor
- Form
- Tablets
- Route
- Oral
- Legal status
- Prescription-only medicine
Availability and supply rules vary by country
Trade names by country: United States · Canada
Australia: · Full directory
What allopurinol is and how it works
Allopurinol is a xanthine oxidase inhibitor that reduces uric acid production by blocking the enzyme that converts hypoxanthine and xanthine to uric acid. It is used to lower uric acid levels in conditions such as gout, certain kidney stones, and in patients receiving cancer treatment that causes high uric acid. (1) (2)
Allopurinol is a long-term preventive treatment; it does not treat acute gout attacks and may initially trigger flares. A doctor must determine the correct dose and monitor treatment. Do not start or stop allopurinol without medical guidance.
Mechanism of action: how allopurinol works
Allopurinol is a xanthine oxidase inhibitor that blocks the conversion of hypoxanthine and xanthine to uric acid, thereby reducing uric acid production. (1) (2)
What allopurinol is used for
Gout and urate deposition conditions
Allopurinol is used for chronic/prophylactic management of gout (lowering uric acid to prevent future attacks) in the US, and for gout and urate/uric acid deposition conditions in the UK. It is not used to treat an acute gout attack that is already underway. (1) (2)
Hyperuricemia secondary to malignancy or chemotherapy
In the US, allopurinol is approved for hyperuricemia resulting from malignancy or its treatment (e.g., chemotherapy). (1)
Recurrent uric acid kidney stones
Allopurinol is indicated for recurrent uric acid nephrolithiasis in the US, and for uric acid kidney stones in the UK. (1) (2)
Asymptomatic hyperuricemia (selected cases)
In the US, allopurinol may be used for asymptomatic hyperuricemia in specific clinical scenarios. (1)
Enzyme disorders causing urate overproduction
In the UK, allopurinol is indicated for management of inherited enzyme disorders such as Lesch-Nyhan syndrome and glycogen storage disease, which lead to excessive urate production. (2)
2,8-dihydroxyadenine (2,8-DHA) renal stones
Allopurinol is used in the UK for management of 2,8-DHA renal stones. (2)
Recurrent calcium oxalate renal stones with hyperuricosuria
In the UK, allopurinol is indicated for recurrent calcium oxalate kidney stones when hyperuricosuria persists despite fluid and dietary measures. (2)
Before taking allopurinol
Do not take / not appropriate for
- UK SmPC: hypersensitivity to allopurinol or any ingredient in the formulation is a contraindication. Tell your prescriber if this applies to you. (UK SmPC) (2)
- Allopurinol should not be started during an acute gout attack (UK SmPC). (all indications) (2)
- Seek immediate medical attention at the first sign of a severe skin reaction — rash, blisters, fever, painful urination, blood in the urine, eye irritation, or swelling of the lips or mouth. The clinician providing urgent care should advise whether allopurinol should be continued, withdrawn, or restarted; do not make that decision yourself. (all indications) (1) (2)
Tell your clinician about
- Current or past liver or kidney problems, including if you are on dialysis.
- Your ethnic background, especially if you have Han Chinese, Thai, Korean, or other Asian ancestry, because of a genetic risk factor (HLA-B*5801) that increases the chance of severe skin reactions.
- All medications you take, particularly azathioprine, mercaptopurine, warfarin, thiazide diuretics, ACE inhibitors, ampicillin, amoxicillin, or bendamustine.
- If you are pregnant, planning to become pregnant, or breastfeeding.
- Any signs of infection, unexplained bruising or bleeding, sore throat, or fever.
- Whether you have been prescribed colchicine or NSAIDs for gout prophylaxis.
How to take allopurinol
- Allopurinol is taken orally, usually once daily or in divided doses as directed by your doctor.
- The starting dose is low (typically 100 mg to 200 mg per day) to reduce the risk of side effects and gout flares.
- The dose is then increased gradually, based on your uric acid levels and tolerance, until the target uric acid level is reached (commonly less than 6 mg/dL in the US).
- The maximum recommended daily dose is 800 mg, given in divided doses; however, your doctor may prescribe higher doses in certain situations.
- For patients with moderate-to-severe kidney impairment (US label) or severe kidney impairment (UK SmPC), the dose is reduced; your prescriber will determine the right dose for your kidney function.
- Your doctor may prescribe an anti-inflammatory medicine (such as colchicine or an NSAID) for at least the first month of treatment to prevent gout flares.
- Do not change your dose or stop taking allopurinol without your doctor's instruction.
Procedures and treatment changes
Tell the treating team before surgery, procedures, or any medicine change. Do not alter treatment without the responsible clinician. (1) (2)
Missed dose
No specific missed-dose instruction was found in the reviewed official prescribing information; seek guidance from your doctor or pharmacist.
Overdose
No specific overdose management information was captured from the reviewed sources; seek emergency medical attention if you suspect an overdose.
Side effects
Rash is a common adverse reaction to allopurinol; gastrointestinal upset can also occur. Serious skin and liver reactions need urgent attention. Gout flares may occur during initial treatment.
Skin rash or itching
What to notice: Any new rash or itching.
What to do: Seek immediate medical attention for any rash or skin reaction, even if it seems mild — allopurinol can cause severe skin reactions that may start this way. (1) (2)
Gastrointestinal effects
What to notice: Nausea and vomiting (UK SmPC); diarrhea and abdominal discomfort (US label).
What to do: Report persistent or severe symptoms to your doctor. (1) (2)
Headache
What to notice: Generalized headache.
What to do: Discuss with your doctor if it interferes with daily activities. (1)
Elevated liver enzymes
What to notice: Detected through blood tests during routine monitoring.
What to do: Your doctor will monitor liver function periodically. (1)
Gout flare
What to notice: Increased joint pain, swelling, and redness, which may occur when allopurinol treatment is starting.
What to do: Tell your prescriber if you have a gout flare while starting allopurinol. They will advise on managing the flare and on whether to continue allopurinol — do not decide this yourself. (1) (2)
Bone marrow suppression
What to notice: Unexplained bruising or bleeding, persistent sore throat, fever, or signs of infection.
Hepatotoxicity
What to notice: Liver problems are usually detected through routine blood testing.
What to do: Attend your scheduled liver function tests. Contact your doctor if you have any concerns. (1) (2)
Serious warnings
Severe skin reactions (SJS, TEN, DRESS) — emergency
Symptoms: Skin rash, blisters, fever, painful urination, blood in the urine, eye irritation, swelling of the lips or mouth, or other signs of hypersensitivity.
Action: Seek emergency medical attention immediately. The clinician assessing you should decide whether allopurinol needs to be withdrawn and whether it can be restarted in future — this decision should not be made on your own. (1) (2)
Interactions
| Medicine or test | Effect | Action |
|---|---|---|
| Azathioprine and mercaptopurine | Allopurinol significantly increases the toxicity of azathioprine and mercaptopurine. | Tell your prescriber if you are taking azathioprine or mercaptopurine. If concurrent use is required, your prescriber will manage this, which may include reducing the azathioprine/mercaptopurine dose (product labeling describes a reduction to 25% of the usual dose) and monitoring you carefully. Do not adjust these doses yourself. (1) (2) |
| Warfarin | Allopurinol may increase the anticoagulant effect of warfarin. | Tell your prescriber if you are taking warfarin. They will monitor your INR and decide whether your warfarin dose needs adjusting — do not change your own dose. (1) (2) |
| Thiazide diuretics | May increase hyperuricemia and contribute to hypersensitivity risk, especially with renal impairment. | Tell your prescriber if you are taking a thiazide diuretic. They will monitor your uric acid levels and renal function and use the combination with caution. (1) (2) |
| Ampicillin and amoxicillin | Increased risk of ampicillin-associated skin rash. | Tell your prescriber if you are taking or are prescribed ampicillin or amoxicillin. They will decide whether an alternative antibiotic is appropriate. (1) (2) |
| ACE inhibitors | Possible interaction affecting renal function/hypersensitivity risk, especially in renal impairment. | Tell your prescriber if you are taking an ACE inhibitor. They will monitor your renal function and assess the risk before starting or continuing either medicine. (1) (2) |
| Bendamustine | May increase the risk of serious skin reactions with allopurinol. | Tell your prescriber if you are taking or starting bendamustine. They will monitor you closely for skin reactions. (1) |
Pregnancy, breastfeeding, kidney/liver function, age
Children and adolescents
Allopurinol dosing for children under 15 years is typically 10-20 mg/kg/day up to a maximum of 400 mg daily, as per UK guidance. US dosing may differ; a specialist should determine the appropriate dose. (2)
Pregnancy and breastfeeding
Allopurinol is generally considered acceptable in pregnancy when management of hyperuricemia is clinically necessary (US). However, it is excreted in breast milk; caution is advised for nursing infants (US) and breastfeeding is not recommended in the UK due to excretion. Discuss risks and benefits with your doctor. (1) (2)
Renal impairment
Allopurinol doses need to be reduced in people with kidney disease to avoid drug accumulation, including specific guidance for severe impairment and dialysis. Your prescriber will determine the right dose for your level of kidney function — this is not something to work out on your own. (1) (2)
Genetic risk (HLA-B*5801)
People with the HLA-B*5801 gene variant, particularly those of Han Chinese (up to 20%), Thai, Korean, or other Asian ancestry, are at increased risk of severe skin reactions. Screening for this genotype may be considered before starting allopurinol in at-risk populations. (1) (2)
Monitoring
Before starting
- Your prescriber will avoid starting allopurinol during an acute gout attack (per the UK SmPC).
- You will be asked to report any rash immediately.
- Consider HLA-B*5801 testing for patients from high-risk ethnic groups (e.g., Han Chinese, Thai, Korean), per the sources reviewed for this page.
During treatment
- Monitor serum uric acid levels and titrate dose to achieve target (commonly <6 mg/dL in US guidance).
- Liver function is monitored periodically; your prescriber uses your kidney function to guide dose selection.
- Watch for signs of skin reactions or bone marrow suppression.
- Provide gout flare prophylaxis with anti-inflammatory agents (e.g., colchicine or NSAID) for at least the first month.
- Signs of severe hypersensitivity require urgent medical assessment; the treating clinician will determine whether allopurinol must be permanently withdrawn.
Storage
No specific storage guidance was extracted from the reviewed sources. Follow the instructions on the medication label or your pharmacist's advice.
Professional information
Clinician-facing context only. Use the current local indication, dosing table, and product-specific guidance.
United States
Indication: Gout and hyperuricemia
Dose summary: Starting dose 100-200 mg daily; titrate by 100 mg increments weekly based on serum uric acid levels (target <6 mg/dL). Maximum daily dose 800 mg in divided doses. Refer to the current full US label.
Renal context: US label contains a specific dose-adjustment table for impaired renal function (creatinine clearance-based); not fully extracted in this research. (1)
United Kingdom
Indication: Gout, urate deposition, and other licensed conditions
Dose summary: Start 100 mg/day to reduce adverse reactions. Mild conditions: 100–200 mg/day; moderately severe: 300–600 mg/day; severe: 700–900 mg/day. Paediatric (<15 years): 10–20 mg/kg/day (max 400 mg). Severe renal impairment: <100 mg/day or 300–400 mg post-dialysis 2-3 times/week. Consider therapeutic monitoring of plasma oxipurinol (target <100 µmol/L).
Renal context: Reduce dose in severe renal impairment; less than 100 mg daily or 300–400 mg after dialysis 2-3 times per week. (2)
Hepatic guidance
Liver function should be monitored during treatment.
Overdose note
No specific overdose management information was found in the sources reviewed for this page. (1) (2)
Frequently asked questions
Can allopurinol treat an acute gout attack?
No — allopurinol is not indicated for an acute gout attack that is already underway, and it may even trigger flares when first started. Your doctor will manage any acute attack separately. (1) (2)
What should I do if I develop a rash while taking allopurinol?
Seek immediate medical attention if you develop a rash while taking allopurinol — even a mild rash can be the first sign of a severe reaction. Let the clinician you see know you are taking allopurinol so they can advise on whether to continue or stop it. (1) (2)
Why do I need regular blood tests while on allopurinol?
Blood tests help monitor your uric acid levels and liver function, and your kidney function is used to guide your dose — this helps ensure the medicine is working safely and effectively. (1) (2)
What is the mechanism of action of allopurinol?
Allopurinol is a xanthine oxidase inhibitor that blocks the conversion of hypoxanthine and xanthine to uric acid, thereby reducing uric acid production. (1) (2)
References
- ALLOPURINOL tablets — prescribing informationU.S. Food and Drug Administration · United States · dated 2024 · accessed 2026-08-05 · source 1
- Allopurinol 100 mg tablets — Summary of Product Characteristicselectronic Medicines Compendium (UK) · United Kingdom · accessed 2026-08-05 · source 2
- ALLOPURINOL TABLET [PD-RX PHARMACEUTICALS, INC.] — US prescribing information (DailyMed SPL)U.S. National Library of Medicine (DailyMed) · US · accessed 2026-08-14 · source 3
- Allopurinol — patient drug information (MedlinePlus)U.S. National Library of Medicine (MedlinePlus) · US · accessed 2026-08-14 · source 4
- Allopurinol — FDA approval record (Drugs@FDA ANDA075798)U.S. Food and Drug Administration · US · accessed 2026-08-14 · source 5
- allopurinol — RxNorm normalized drug concept (RXCUI 519)U.S. National Library of Medicine (RxNorm) · US · accessed 2026-08-14 · source 6
Brand names by country
Single-ingredient allopurinol names are shown separately by country. Product availability, strengths, and supply rules can change; combination products are not included here.
Priority countries
United States
- Aloprim500 mg/25mL · mylan institutional llc
Canada
- ZYLOPRIM