Allopurinol Drug Profile

What is Allopurinol?

Allopurinol is a xanthine oxidase inhibitor medication primarily used to prevent gout attacks and manage conditions associated with high uric acid levels. It belongs to a class of drugs that reduce the production of uric acid in the body. This medication is typically prescribed for long-term management rather than acute treatment of gout flares.

Uses

Allopurinol has several approved medical uses:

• Chronic gout prevention: Reduces frequency and severity of gout attacks by lowering uric acid levels in the blood
• Hyperuricemia management: Treats elevated uric acid levels that may result from various medical conditions or treatments
• Kidney stone prevention: Helps prevent calcium oxalate and uric acid kidney stones in patients with recurrent stone formation
• Cancer treatment support: Prevents tumor lysis syndrome in patients receiving chemotherapy for certain cancers
• Enzyme deficiency disorders: Manages hyperuricemia associated with genetic conditions affecting purine metabolism

How it works

Allopurinol works by inhibiting xanthine oxidase, an enzyme responsible for converting purines into uric acid. By blocking this enzyme, the medication significantly reduces the amount of uric acid produced in the body. This lower uric acid level helps prevent the formation of uric acid crystals in joints and tissues, which are responsible for gout attacks and other complications.

Side effects

Common side effects include:

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• Skin rash
• Nausea and vomiting
• Diarrhea
• Drowsiness
• Headache
• Metallic taste
• Muscle pain
• Fever

Serious side effects requiring immediate medical attention:

• Severe skin reactions (Stevens-Johnson syndrome, toxic epidermal necrolysis)
• Liver damage with symptoms like yellowing of skin or eyes
• Severe allergic reactions with difficulty breathing
• Blood disorders affecting white blood cells or platelets
• Kidney problems with decreased urination

Warnings and precautions

• Kidney and liver function: Patients with impaired kidney or liver function require dose adjustments and regular monitoring, as the medication can accumulate and cause toxicity
• Initial gout flares: Allopurinol may initially trigger gout attacks when first started, so prophylactic anti-inflammatory medications are often prescribed concurrently
• Genetic screening: Patients of Asian descent, particularly those of Han Chinese, Korean, or Thai ethnicity, should undergo genetic testing for HLA-B*5801 allele before starting treatment due to increased risk of severe skin reactions
• Pregnancy and breastfeeding: Limited safety data exists for use during pregnancy and breastfeeding; potential benefits must be weighed against potential risks
• Gradual initiation: Treatment should start with low doses and be gradually increased to minimize adverse reactions and allow the body to adjust

Interactions

Allopurinol has several important drug interactions:

• Warfarin: May enhance anticoagulant effects, requiring more frequent INR monitoring and potential dose adjustments
• Azathioprine and mercaptopurine: Significantly increases levels of these immunosuppressive drugs, requiring substantial dose reductions to prevent toxicity
• Ampicillin and amoxicillin: Increases risk of skin rashes when used concurrently with these antibiotics
• Thiazide diuretics: May reduce kidney function and increase allopurinol levels, potentially leading to toxicity
• ACE inhibitors: Combined use may increase risk of kidney problems and hypersensitivity reactions
• Theophylline: Allopurinol can increase theophylline levels, requiring dose adjustments and monitoring for toxicity
• Cyclophosphamide: May increase bone marrow toxicity when used together
• Iron supplements: Allopurinol may increase iron storage in the liver, requiring monitoring in patients with iron overload conditions

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Dosage

Typical adult dosages vary based on the condition being treated and individual patient factors. For gout prevention, treatment usually begins with 100 mg daily and may be gradually increased to 200-300 mg daily, with some patients requiring up to 600-800 mg daily for optimal uric acid control. For preventing tumor lysis syndrome, higher doses of 600-800 mg daily may be used for short periods. Patients with kidney impairment require significant dose reductions. All dosing should be individualized and determined by a healthcare provider based on uric acid levels, kidney function, and treatment response.

Sources: FDA DailyMed drug labels (public domain), BNF, WHO Essential Medicines List. This article is for informational purposes only and does not constitute medical advice. Always consult your healthcare provider before starting or stopping any medication.

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