Allopurinol is a xanthine oxidase inhibitor prescribed for the long-term management of hyperuricemia, particularly in patients with gout, kidney stones, or those undergoing certain chemotherapy regimens. By reducing the production of uric acid, it helps prevent painful gout attacks and the formation of tophi. This medication requires consistent use and medical supervision to achieve optimal therapeutic outcomes while minimizing risks.

Features

• Active ingredient: Allopurinol
• Available in 100 mg and 300 mg tablet formulations
• Requires prescription; not available over-the-counter
• Generic versions are widely available
• Typically administered orally once daily
• Bioavailability approximately 90% when taken on empty stomach
• Half-life of approximately 1-2 hours (active metabolite oxypurinol: 18-30 hours)
• Metabolized primarily in the liver
• Excreted mainly through renal pathway

Benefits

• Prevents recurrent acute gout attacks by maintaining serum uric acid below saturation point
• Reduces formation and promotes gradual resolution of tophi (urate crystal deposits)
• Decreases risk of uric acid nephrolithiasis (kidney stones)
• Helps prevent tumor lysis syndrome in patients receiving chemotherapy
• May slow progression of chronic kidney disease associated with hyperuricemia
• Provides predictable, dose-dependent reduction in uric acid production

Common use

Allopurinol is primarily indicated for the management of hyperuricemia in patients with gout, either in the form of recurrent acute attacks, chronic gouty arthritis, or tophaceous gout. It is also used for managing hyperuricemia secondary to malignancies, particularly during chemotherapy where rapid cell turnover may cause tumor lysis syndrome. Additionally, it is prescribed for patients with recurrent uric acid kidney stones and those with certain enzyme deficiencies that cause hyperuricemia, such as Lesch-Nyhan syndrome. The medication is not intended for treatment of acute gout attacks but rather for prophylaxis against future episodes.

Dosage and direction

Initial dosing typically begins with 100 mg once daily, with gradual titration upward by 100 mg every 1-4 weeks until target serum uric acid level (<6 mg/dL) is achieved. Maintenance doses typically range from 200-600 mg daily, though some patients may require up to 800 mg daily divided into 2-3 doses. For patients with renal impairment, dosage adjustment is necessary based on creatinine clearance: 200 mg daily for CrCl 60-89 mL/min, 100 mg daily for CrCl 30-59 mL/min, and 100 mg every 2-3 days for CrCl <30 mL/min. The medication should be taken with plenty of water (at least 8 ounces) to ensure adequate hydration and minimize risk of kidney stone formation. It may be taken with food if gastrointestinal upset occurs, though absorption is slightly reduced. Therapy should be initiated after acute gout attack has resolved, often with concurrent NSAID or colchicine prophylaxis during the first 3-6 months to prevent flare-ups.

Precautions

Patients should maintain adequate hydration (2-3 liters daily) to prevent uric acid nephrolithiasis. Regular monitoring of serum uric acid levels, liver function tests, complete blood count, and renal function is recommended, particularly during the first few months of therapy. Caution is advised in patients with pre-existing hepatic impairment or bone marrow suppression. Allopurinol should be discontinued immediately if rash develops, as this may indicate severe hypersensitivity reaction. Patients with HLA-B*5801 allele are at increased risk for severe cutaneous adverse reactions; genetic testing may be considered in high-risk populations. Gradual dose titration is essential to minimize initial gout flares. Concomitant use with azathioprine or mercaptopurine requires significant dose reduction of these medications due to metabolic interactions.

Contraindications

Allopurinol is contraindicated in patients with known hypersensitivity to allopurinol or any component of the formulation. It should not be initiated during an acute gout attack, as it may prolong the acute episode. The medication is contraindicated in patients who have previously experienced severe skin reactions to allopurinol, including Stevens-Johnson syndrome, toxic epidermal necrolysis, or drug reaction with eosinophilia and systemic symptoms (DRESS). Concomitant use with didanosine is generally contraindicated due to increased risk of didanosine toxicity. The medication should not be used in asymptomatic hyperuricemia except in patients receiving cancer chemotherapy.

Possible side effect

Common side effects include skin rash (approximately 2% of patients), nausea, vomiting, diarrhea, and drowsiness. Less frequent adverse effects include elevated liver enzymes, leukopenia, thrombocytopenia, and peripheral neuropathy. Serious but rare side effects include severe hypersensitivity reactions (2-5 per 10,000 patients) characterized by fever, eosinophilia, rash, hepatitis, and renal impairment. Other rare serious reactions include Stevens-Johnson syndrome, toxic epidermal necrolysis, vasculitis, and bone marrow suppression. Some patients may experience acute gout flares during initial therapy, which typically diminish with continued treatment. Alopecia and taste perversion have been reported in some cases.

Drug interaction

Allopurinol significantly potentiates the effects of azathioprine and mercaptopurine by inhibiting their metabolism, necessitating dose reduction of these drugs by approximately 75%. It may increase the risk of bone marrow suppression when used with other myelosuppressive agents. Concurrent use with ampicillin or amoxicillin increases the incidence of skin rash. Allopurinol may prolong the half-life of warfarin, requiring closer monitoring of INR. It can increase serum concentrations of theophylline and cyclosporine. Diuretics, particularly thiazides, may decrease the excretion of oxypurinol, potentially increasing allopurinol toxicity. Concurrent use with iron salts may cause hepatic iron accumulation.

Missed dose

If a dose is missed, it should be taken as soon as remembered unless it is almost time for the next scheduled dose. In that case, the missed dose should be skipped and the regular dosing schedule resumed. Doubling the dose to make up for a missed dose is not recommended. Consistency in dosing is important for maintaining stable uric acid levels, but occasional missed doses are unlikely to significantly affect long-term control. Patients should maintain their usual hydration practices even if a dose is missed.

Overdose

Symptoms of overdose may include nausea, vomiting, diarrhea, and dizziness. In severe cases, acute renal failure, hepatitis, bone marrow suppression, and exfoliative dermatitis may occur. Management is primarily supportive and symptomatic. Hemodialysis may be effective in removing allopurinol and its metabolites, particularly in patients with renal impairment. Gastric lavage may be considered if presentation is early after ingestion. Patients should be monitored for hypersensitivity reactions even in overdose scenarios. Maintenance of adequate urine output is important to prevent acute uric acid nephropathy.

Storage

Store at controlled room temperature (20-25°C or 68-77°F) in a dry place protected from light and moisture. Keep in the original container with the lid tightly closed. Do not store in bathroom cabinets where humidity levels may fluctuate. Keep out of reach of children and pets. Do not use if tablets show signs of discoloration, cracking, or if the expiration date has passed. Proper disposal of unused medication through take-back programs is recommended to prevent environmental contamination and accidental ingestion.

Disclaimer

This information is for educational purposes only and does not constitute medical advice. Allopurinol is a prescription medication that should be used only under the supervision of a qualified healthcare provider. Individual response to medication may vary, and proper medical supervision is essential for safe and effective use. Patients should not adjust dosage or discontinue medication without consulting their healthcare provider. This information is not exhaustive and does not cover all possible uses, directions, precautions, or interactions.

Reviews

Clinical studies demonstrate that allopurinol effectively reduces serum uric acid levels in approximately 80-90% of patients with appropriate dosing. Long-term use shows significant reduction in gout flare frequency, with studies indicating 80-90% reduction in acute attacks after 1-2 years of therapy. Patient satisfaction surveys indicate improved quality of life scores related to reduced pain and increased mobility. However, approximately 20% of patients may experience initial gout flares during therapy initiation. The medication receives generally positive expert reviews for its efficacy in chronic gout management, though the need for careful patient selection and monitoring is consistently emphasized in the medical literature.