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 cancer treatments. By reducing the production of uric acid, it addresses the underlying metabolic imbalance rather than merely alleviating symptoms. This medication requires consistent use and medical supervision to achieve optimal therapeutic outcomes and minimize potential adverse effects. Proper patient education on dosage, interactions, and monitoring is essential for successful treatment.

Features

• Active ingredient: Allopurinol
• Drug class: Xanthine oxidase inhibitor
• Available forms: Oral tablets (100 mg, 300 mg)
• Prescription status: Rx-only
• Mechanism: Inhibits xanthine oxidase, reducing uric acid synthesis
• Bioavailability: Approximately 90% when administered orally
• Half-life: Allopurinol: 1–3 hours; Oxypurinol (active metabolite): 18–30 hours
• Metabolism: Hepatic, to active metabolite oxypurinol
• Excretion: Primarily renal

Benefits

• Reduces frequency and severity of gout attacks by lowering serum uric acid levels
• Prevents formation of new uric acid kidney stones and may reduce existing stone size
• Decreases risk of urate nephropathy and joint damage from chronic hyperuricemia
• Allows for long-term management of hyperuricemia associated with chemotherapy
• May improve quality of life by reducing painful gout flares and joint inflammation
• Provides predictable pharmacokinetics with once-daily dosing in most patients

Common use

Allopurinol is primarily indicated for the management of hyperuricemia in patients with gout, whether manifested as recurrent acute attacks, tophi, joint destruction, or uric acid nephrolithiasis. It is also used for managing hyperuricemia secondary to blood dyscrasias and malignancies, particularly during cytotoxic therapy where rapid cell turnover may cause tumor lysis syndrome. The medication is not intended for treating acute gout attacks but rather for prophylaxis against future episodes. Off-label uses include prevention of calcium oxalate stones in hyperuricosuric patients and management of Lesch-Nyhan syndrome.

Dosage and direction

Initial dosage typically begins with 100 mg daily, increased weekly by 100 mg until serum uric acid falls below 6 mg/dL. Maintenance doses range from 200-600 mg daily for mild gout, with severe cases potentially requiring up to 800 mg daily divided into 2-3 doses. For patients with renal impairment, dosage adjustment is necessary: CrCl 10-20 mL/min: 200 mg daily maximum; CrCl 3-10 mL/min: 100 mg daily maximum; CrCl <3 mL/min: 100 mg with extended intervals. Administer with food to minimize gastric upset and maintain adequate hydration (2-3 liters daily). During initial therapy, concomitant NSAID or colchicine prophylaxis is recommended for the first 3-6 months to prevent acute gout flares.

Precautions

Regular monitoring of serum uric acid levels, renal function, and liver enzymes is essential throughout therapy. Use with caution in patients with hepatic impairment, as allopurinol is metabolized in the liver. Hydration status should be maintained to prevent crystallization of uric acid in the kidneys. Patients should be advised that acute gout attacks may increase during initial therapy and that the medication should not be discontinued during such episodes. Caution is warranted in patients with bone marrow suppression or those receiving concurrent drugs that affect bone marrow function. Periodic complete blood counts are recommended during prolonged therapy.

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 experienced severe skin reactions such as Stevens-Johnson syndrome or toxic epidermal necrolysis with previous allopurinol use. Concomitant use with didanosine is contraindicated due to increased risk of didanosine-related adverse effects. The drug is not recommended for use in asymptomatic hyperuricemia except in patients undergoing cancer chemotherapy.

Possible side effect

Common adverse reactions include skin rash (approximately 2%), nausea, vomiting, diarrhea, and drowsiness. More serious but less frequent side effects include hepatitis (elevated transaminases, jaundice), peripheral neuritis, bone marrow suppression (leukopenia, thrombocytopenia, anemia), and vasculitis. The most concerning adverse reaction is severe hypersensitivity syndrome, characterized by fever, rash, eosinophilia, hepatitis, and renal impairment, which occurs in approximately 0.4% of patients. Other reported effects include alopecia, cataracts, and taste perversion. Elderly patients may experience increased frequency of some adverse reactions.

Drug interaction

Allopurinol potentiates the effects of azathioprine and mercaptopurine by inhibiting their metabolism, requiring dose reduction of these drugs by 65-75%. It may increase the risk of bone marrow suppression when used with other myelosuppressive agents. Concurrent use with ampicillin/amoxicillin increases the incidence of skin rash. Allopurinol may prolong the half-life of anticoagulants like warfarin, necessitating closer INR monitoring. Diuretics, especially thiazides, may increase allopurinol concentrations and the risk of hypersensitivity reactions. The drug may increase serum levels of theophylline and cyclosporine.

Missed dose

If a dose is missed, it should be taken as soon as remembered unless it is nearly time for the next scheduled dose. In that case, the missed dose should be skipped, and the regular dosing schedule resumed. Patients should not double the dose to make up for a missed one. 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 be educated about the importance of regular dosing while understanding that single missed doses generally don’t require special measures.

Overdose

Symptoms of overdose may include nausea, vomiting, diarrhea, and dizziness. In severe cases, acute renal failure, hepatitis, and bone marrow suppression may occur. Management involves gastric lavage if presentation is early, followed by supportive care with attention to hydration and electrolyte balance. Hemodialysis is effective in removing allopurinol and its active metabolite oxypurinol, and should be considered in cases of significant overdose, particularly in patients with renal impairment. There is no specific antidote for allopurinol overdose.

Storage

Store at controlled room temperature (20-25°C or 68-77°F) in a tightly closed container, protected from light and moisture. Keep out of reach of children and pets. Do not store in bathroom cabinets where humidity may affect stability. Discard any medication that has expired or shows signs of deterioration. Do not flush medications down the toilet or pour them into drainage unless instructed to do so. Proper disposal through medication take-back programs is recommended.

Disclaimer

This information is provided for educational purposes only and does not constitute medical advice. Individual patient needs may vary, and healthcare providers should be consulted for specific medical recommendations. The prescribing physician should be aware of the complete medical history and concurrent medications before initiating therapy. Actual product labeling and prescribing information should be consulted for comprehensive guidance. This information is not exhaustive and may not include all possible uses, directions, precautions, or interactions.

Reviews

Clinical studies demonstrate that allopurinol effectively reduces serum uric acid levels to target ranges in approximately 80-90% of patients with chronic gout when appropriately dosed. Long-term use shows significant reduction in gout attack frequency, with studies reporting 80-90% reduction in acute flares after 6-12 months of therapy. Patient satisfaction surveys indicate improved quality of life measures related to reduced pain and increased mobility. However, approximately 20% of patients may experience mild adverse effects, with 3-5% discontinuing therapy due to side effects. The medication receives generally positive expert reviews for its efficacy in chronic uric acid management when used according to established guidelines.