Allopurinol
In brief
- Allopurinol is a prescription-only medicine (POM) in the UK and should be supplied only on a valid prescription and under medical supervision.
- Allopurinol is used to treat chronic gout and hyperuricaemia, to prevent uric acid kidney stones and for tumour lysis syndrome prophylaxis; it is a xanthine oxidase inhibitor that reduces uric acid production.
- Typical adult dosing starts at 100 mg once daily and is titrated according to serum uric acid — usual maintenance 200–300 mg/day (mild) or 400–600 mg/day (severe); maximum doses up to 800 mg/day in specialist care; dose reductions are required in renal impairment (e.g. CrCl <20 mL/min often limited to ~100 mg/day). Children (when indicated) 10–20 mg/kg/day, max ~400 mg/day.
- Administered orally as tablets (commonly 100 mg and 300 mg); no routine injectable forms.
- Serum uric acid reduction is often detectable within a few days (2–3 days), but clinical benefit (fewer flares, tophi reduction) usually takes weeks to months; do not expect immediate relief of an acute gout attack.
- Because the active metabolite (oxypurinol) is long‑acting, once‑daily dosing provides 24‑hour urate lowering; full therapeutic effect is maintained with regular daily dosing.
- Avoid excessive alcohol: alcohol raises uric acid and can precipitate gout flares and may worsen liver effects — minimise alcohol intake while using allopurinol.
- The most common side effect is a skin rash (which may signal a serious hypersensitivity reaction — stop the drug and seek urgent medical advice); other common effects include gastrointestinal upset and mild liver enzyme elevations.
- Would you like to try allopurinol without a prescription?
Legal status and availability in the UK
Allopurinol is a prescription-only medicine (POM) in the UK.
In our online pharmacy, allopurinol is available without a prescription, with discreet delivery to the United Kingdom in 9–21 days.
Basic allopurinol information
- INN (international nonproprietary name): Allopurinol.
- Brand names available in the United Kingdom: allopurinol generics supplied by Teva, Sandoz, Mylan, Accord and Zentiva, and the originator brand Zyloric.
- ATC code: M04AA01 (musculo-skeletal system; antigout preparations; preparations inhibiting uric acid production).
- Forms and dosages: tablets 100 mg and 300 mg.
- Manufacturers in the United Kingdom: Teva, Sandoz, Mylan, Accord, Zentiva and Sanofi (Zyloric).
- Registration status in the United Kingdom: licensed by the MHRA; prescription-only medicine (POM).
- OTC / Rx classification: Prescription-only medicine (POM).
Supply and packaging
Allopurinol is supplied on prescription, usually from a GP or hospital specialist. Tablets in 100 mg and 300 mg strengths are the standard pack formats in the UK, usually in blister packs.
A patient may receive a different manufacturer on repeat prescriptions; the INN formulations are equivalent apart from minor excipient differences.
Product identity and mechanism
INN, classification and pharmacology
The International Nonproprietary Name is allopurinol.
Allopurinol is classified under ATC code M04AA01 as a preparation inhibiting uric acid production.
It belongs to the xanthine oxidase inhibitors and works by blocking the enzyme xanthine oxidase, reducing the synthesis of uric acid.
Practical meaning for patients
Blocking uric acid synthesis lowers serum urate and over time reduces gouty arthritis, tophi and the risk of uric acid kidney stones.
This mechanism explains why the effect is preventive and why serum urate testing is required to guide dose titration.
Allopurinol is registered with regulatory authorities including the MHRA and is included on the WHO Essential Medicines List, which can reassure patients about its established role.
Licensed indications and everyday uses
Primary clinical uses in pharmacy practice
Allopurinol is authorised for chronic gout due to hyperuricaemia, prevention of uric acid nephrolithiasis and prophylaxis of tumour lysis syndrome in high‑risk chemotherapy patients.
It is not indicated for treating an acute gout attack and should not be started during a flare.
For chronic gout the usual approach is long‑term therapy with dose titration to a target serum urate level.
Off‑label and specialist uses
Paediatric use is limited and generally confined to tumour lysis prophylaxis or rare inherited disorders, using weight‑based dosing (typically 10–20 mg/kg/day, max ~400 mg/day).
Specialist oncology teams commonly use short high‑dose regimens for tumour lysis syndrome prevention, often in the 600–800 mg/day range divided over the day.
Co‑prescribed agents such as colchicine are sometimes used for flare prophylaxis.
Available formulations, packaging and dosing options
Tablet strengths and common pack formats
Oral tablets are the standard formulation, with 100 mg and 300 mg as the standard strengths.
Packs are typically blistered, which helps with adherence and protecting tablets from moisture and light.
Injectable or topical forms are not used in routine clinical practice.
Tablet strengths in practice
100 mg tablets are used for initial titration and 300 mg tablets for maintenance. If a prescriber recommends two doses of 150 mg equivalent, ask the pharmacist about splitting 300 mg tablets or using multiple 100 mg tablets for convenience.
Dosing strategy and dose adjustment
Starting doses and titration
Initiate at a low dose and titrate according to serum uric acid levels with a common starting dose of 100 mg once daily.
Most adults require maintenance in the region of 200–300 mg daily, with severe hyperuricaemia sometimes needing 400–600 mg daily.
Specialist cases may go up to 800 mg/day with specialist oversight and repeat monitoring.
Renal, hepatic and special‑population adjustments
Renal impairment requires dose reductions; in severe renal dysfunction (CrCl <20 mL/min) doses are often limited to 100 mg/day and alternative therapies may be considered.
Elderly patients should start at the lowest effective dose and undergo renal monitoring.
Hepatic impairment requires caution and follow‑up liver function testing during therapy.
Initiation protocols and concomitant therapy
Preventing initial gout flares
Starting allopurinol can paradoxically precipitate gout flares during the early weeks and months of therapy.
Many clinicians recommend prophylaxis with low‑dose colchicine or an NSAID for 3–6 months when initiating urate‑lowering therapy, unless contraindicated.
Tumour lysis prophylaxis follows different protocols with higher short‑term dosing and should be coordinated with oncology teams.
Before starting
- Before starting: the prescriber confirms current serum urate and recent renal function, checks for azathioprine/6‑MP therapy, asks about prior severe cutaneous reactions and considers HLA‑B*5801 risk in at‑risk ethnicities.
- When to contact the prescriber: rising creatinine, new rash, signs of systemic hypersensitivity, or if urate remains above target despite dose increases.
Review at 2–4 weeks after starting, then every 3 months until stable, is advisable, with prophylaxis and titration tailored to the individual patient.
Contraindications, genetic risks and red flags
Absolute and relative contraindications
Absolute contraindications include known hypersensitivity to allopurinol or excipients and prior severe cutaneous adverse reactions such as Stevens‑Johnson Syndrome or Toxic Epidermal Necrolysis.
Do not initiate during an acute gout attack.
Relative cautions include significant renal or hepatic impairment and pregnancy or breastfeeding where use is only if essential.
HLA‑B*5801 and population risk profiling
HLA‑B*5801 positivity is associated with a higher risk of severe cutaneous adverse reactions, particularly in some Asian populations.
Consider genetic testing in patients from high‑risk ethnic groups prior to initiation where local pathways recommend it.
Red flags: stop the medicine and seek urgent care for widespread rash, mucosal lesions, high fever, yellowing of the skin or reduced urine output.
Side‑effect profile and management
Common mild adverse reactions
Common milder effects are skin rash, nausea, diarrhoea, headache and transient liver enzyme elevations.
An acute gout flare is a recognised short‑term effect of initiation and patients should be reassured and supported to continue therapy under cover if advised by the prescriber.
Recognising and responding to severe reactions
Severe but rare reactions include severe cutaneous adverse reactions (SJS/TEN) and allopurinol hypersensitivity syndrome with systemic involvement.
If a severe rash or systemic signs occur, stop allopurinol immediately and seek urgent hospital assessment.
Report suspected adverse reactions to the MHRA Yellow Card Scheme.
| Symptom | Action |
|---|---|
| Localised mild rash | See the prescriber for review; stop if spreading or systemic symptoms appear |
| Widespread rash, mucosal lesions, fever | Stop medicine immediately and seek urgent medical assessment |
| GI upset or headache | Supportive measures; consider dose timing changes or check interactions |
Drug interactions and safety checks
Major interactions with clinical implications
Azathioprine and mercaptopurine are critical interactions; coadministration with allopurinol increases active metabolites and toxicity risk, requiring dose adjustments or avoidance.
Febuxostat switching and combined nephrotoxins need specialist oversight and renal monitoring.
Monitor warfarin and other narrow therapeutic index drugs where interactions may alter INR or drug levels.
Interaction summary
| Drug | Risk | Action |
|---|---|---|
| Azathioprine / 6‑MP | Marked increase in toxicity | Do not co‑prescribe without specialist dose adjustment; contact prescriber |
| Warfarin | Possible INR changes | Monitor INR after initiation or dose change |
| Nephrotoxic agents | Increased renal injury risk | Ensure renal function monitoring; avoid combinations where possible |
Tell the prescriber about immunosuppressants and recent chemotherapy, and make sure renal function is up to date for higher doses.
Storage, missed dose and overdose guidance
Storage
Store allopurinol below 25°C in its original packaging to protect from light and moisture.
Do not freeze. Keep medicine in the original blister packs until taken to support adherence.
Patient instructions for missed doses and overdose
If a dose is missed, take it as soon as remembered unless the next dose is due; do not double up.
In case of suspected overdose, seek immediate medical attention; supportive care is the mainstay of management.
Advise safe disposal of unused medicines via pharmacy return schemes and local take‑back services.
Alternatives, switches and specialist options
When to consider alternatives
Consider alternatives when a patient has true intolerance or prior severe hypersensitivity to allopurinol.
Febuxostat is an alternative xanthine oxidase inhibitor used when allopurinol is unsuitable, but it carries cardiovascular considerations and normally requires specialist assessment.
Uricosurics such as probenecid require adequate renal function and are less used in older patients.
Comparing allopurinol versus febuxostat and others
| Drug | Mechanism | Indication | Notes |
|---|---|---|---|
| Allopurinol | Xanthine oxidase inhibitor | Chronic gout, TLS prophylaxis | First‑line; renal dose adjustments required |
| Febuxostat | Xanthine oxidase inhibitor | Allopurinol intolerance | Specialist switch; cardiovascular cautions |
| Rasburicase | Urate oxidase enzyme | TLS (rapid reduction) | Used in oncology settings; IV only |
Complex switching, high‑dose regimens or alternative mechanisms call for referral to secondary care.
Delivery across the United Kingdom
| City | Region | Delivery time |
|---|---|---|
| London | Greater London | 9–21 days |
| Birmingham | West Midlands | 9–21 days |
| Manchester | Greater Manchester | 9–21 days |
| Glasgow | Scotland | 9–21 days |
| Leeds | West Yorkshire | 9–21 days |
| Liverpool | Merseyside | 9–21 days |
| Bristol | South West England | 9–21 days |
| Edinburgh | Scotland | 9–21 days |
| Cardiff | Wales | 9–21 days |
| Belfast | Northern Ireland | 9–21 days |
| Nottingham | East Midlands | 9–21 days |
| Sheffield | South Yorkshire | 9–21 days |
| Newcastle Upon Tyne | North East England | 9–21 days |
| Southampton | South East England | 9–21 days |
| Plymouth | Devon | 9–21 days |
