Allopurinol is a xanthine oxidase inhibitor prescribed for the long-term management of hyperuricemia, particularly in patients with gout, tophi, or uric acid nephrolithiasis. By reducing the production of uric acid, it addresses the underlying metabolic cause of these conditions rather than merely treating acute symptoms. This medication is a cornerstone of prophylactic therapy, helping to prevent painful gout flares, joint damage, and renal complications associated with elevated serum urate levels. Proper adherence under medical supervision is essential for achieving optimal therapeutic outcomes.

Features

• Active ingredient: Allopurinol
• Drug class: Xanthine oxidase inhibitor
• Available formulations: Oral tablets (100 mg and 300 mg)
• Prescription status: Requires medical prescription
• Mechanism of action: Inhibits xanthine oxidase, the enzyme responsible for converting hypoxanthine to xanthine and xanthine to uric acid
• Bioavailability: Approximately 90% when administered orally
• Half-life: Allopurinol: 1–3 hours; active metabolite oxipurinol: 18–30 hours
• Excretion: Primarily renal

Benefits

• Reduces frequency and severity of acute gout attacks with continued use
• Prevents formation of new uric acid kidney stones and tophi
• Lowers serum uric acid levels to target range (typically <6 mg/dL)
• May help prevent joint damage and chronic gouty arthropathy
• Reduces risk of urate nephropathy and other renal complications
• Provides long-term management of hyperuricemia associated with cancer chemotherapy

Common use

Allopurinol is primarily indicated for the management of:

• Chronic gout and gouty arthritis
• Hyperuricemia secondary to malignancies or their treatment
• Recurrent uric acid stone formation
• Calcium oxalate calculi when uric acid excretion is elevated

It is not indicated for the treatment of acute gout attacks and may initially exacerbate symptoms if initiated during an acute episode.

Dosage and direction

Dosage must be individualized based on serum uric acid levels, renal function, and therapeutic response.

Initial dose: Typically 100 mg daily, increased weekly by 100 mg until target serum uric acid (<6 mg/dL) is achieved Maintenance dose: 200–600 mg daily for mild gout; 400–800 mg daily for severe tophaceous gout Maximum dose: 800 mg daily (divided doses if >300 mg) Dosing in renal impairment: Requires adjustment based on creatinine clearance:

• CrCl 10–20 mL/min: Max 200 mg daily
• CrCl 3–10 mL/min: Max 100 mg daily
• CrCl <3 mL/min: Dosing interval extended to every 48+ hours

Administer with food to minimize gastric upset. Maintain adequate hydration (2+ liters daily) to prevent xanthine crystalluria.

Precautions

• Monitor renal function and serum uric acid levels regularly
• Perform baseline liver function tests and complete blood count
• May initially precipitate acute gout attacks; concurrent prophylactic colchicine or NSAID therapy recommended during first 3–6 months
• Use with caution in patients with hepatic impairment or history of alcohol abuse
• Caution in patients with bone marrow suppression or receiving cytotoxic drugs
• Skin reactions require immediate medical attention; discontinue at first sign of rash
• Not recommended during pregnancy unless clearly needed (Category C)
• Excreted in breast milk; use caution during lactation

Contraindications

• Hypersensitivity to allopurinol or any component of the formulation
• Patients who have experienced severe allopurinol hypersensitivity syndrome
• Asymptomatic hyperuricemia (except during cytotoxic therapy)
• Concomitant use with didanosine (increased toxicity risk)

Possible side effect

Common (≥1%):

• Skin rash (discontinue immediately)
• Nausea, vomiting, diarrhea
• Elevated liver enzymes
• Drowsiness, headache

Less common:

• Eosinophilia, leukopenia, thrombocytopenia
• Hepatotoxicity
• Peripheral neuropathy
• Cataracts (with long-term use)
• Alopecia

Rare but serious:

• Allopurinol hypersensitivity syndrome (fever, rash, eosinophilia, hepatitis, renal failure)
• Stevens-Johnson syndrome, toxic epidermal necrolysis
• Vasculitis
• Bone marrow suppression

Drug interaction

• Azathioprine/6-mercaptopurine: Allopurinol inhibits metabolism, requiring 65-75% dose reduction
• Warfarin: Enhanced anticoagulant effect; monitor INR closely
• Diuretics: May increase allopurinol toxicity risk
• Ampicillin/amoxicillin: Increased incidence of skin rash
• Theophylline: Increased serum levels; monitoring recommended
• Cyclosporine: Possible increased nephrotoxicity
• ACE inhibitors: Increased risk of hypersensitivity reactions

Missed dose

Take the missed dose as soon as remembered unless it is almost time for the next scheduled dose. Do not double the dose to make up for a missed one. Maintain regular dosing schedule to ensure consistent uric acid suppression.

Overdose

Symptoms may include nausea, vomiting, diarrhea, dizziness, and oliguria. Massive overdose may cause renal failure and hepatotoxicity. Management is supportive with gastric lavage if recent ingestion. Hemodialysis may be effective for removing allopurinol and oxipurinol. Maintain hydration and monitor renal function.

Storage

Store at controlled room temperature (20-25°C/68-77°F) in original container. Protect from light and moisture. Keep tightly closed and out of reach of children. Do not use after expiration date.

Disclaimer

This information is for educational purposes only and does not constitute medical advice. Allopurinol requires prescription and medical supervision. Dosage and treatment decisions must be made by a qualified healthcare professional based on individual patient characteristics. Not all side effects or interactions are listed. Patients should report any adverse effects to their physician promptly.

Reviews

Clinical studies demonstrate allopurinol effectively reduces serum uric acid levels in 85-90% of patients with appropriate dosing. Long-term therapy shows significant reduction in gout flare frequency (70-80% reduction after 1 year), tophi resolution, and prevention of renal complications. The drug is generally well-tolerated with proper monitoring, though hypersensitivity reactions remain a concern requiring vigilance. Most patients achieve target uric acid levels with 300 mg daily, though dosage must be individualized based on therapeutic response and renal function.