Allopurinol is a xanthine oxidase inhibitor used primarily for the long-term management of hyperuricemia and its complications, including chronic gout and tumor lysis syndrome. It is a structural analogue of hypoxanthine and acts by inhibiting the enzyme xanthine oxidase, thereby reducing the production of uric acid. It is a cornerstone therapy in the Indian context for preventing gouty arthritis and uric acid nephropathy.
Adult: Gout/Hyperuricemia: Initial: 100 mg once daily, increase by 100 mg weekly until serum uric acid is <6 mg/dL. Usual maintenance: 200-300 mg/day. For severe disease or tophi: 400-600 mg/day in divided doses. Max: 800 mg/day. Tumor Lysis Prophylaxis: 600-800 mg/day in divided doses, starting 2-3 days before chemotherapy.
Note: Take orally after food to minimize gastric upset. Drink plenty of fluids (at least 2 liters per day) to maintain urine output and reduce risk of renal calculi. Tablets can be crushed if needed. Dose is often taken once daily, but doses above 300mg should be divided.
Allopurinol and its primary active metabolite, oxypurinol, are competitive inhibitors of xanthine oxidase, the enzyme responsible for converting hypoxanthine to xanthine and xanthine to uric acid. This inhibition decreases the total production of uric acid, thereby lowering serum and urinary uric acid concentrations.
Pregnancy: US FDA Category C. Animal studies have shown fetal harm. Use only if potential benefit justifies potential risk to the fetus, primarily for treatment of malignancy-associated hyperuricemia. Not for routine gout management.
Driving: May cause dizziness, drowsiness, or vertigo. Patients should not drive or operate machinery until they know how the medication affects them.
| Azathioprine / Mercaptopurine | Allopurinol inhibits xanthine oxidase, which is involved in the metabolism of these drugs, leading to dangerously increased levels and severe myelosuppression. | Major |
| Didanosine | Increased plasma concentration of didanosine, increasing risk of pancreatitis and neuropathy. | Major |
| Warfarin | May potentiate anticoagulant effect by unknown mechanism; increased INR monitoring required. | Moderate |
| Theophylline / Aminophylline | Increased theophylline levels; risk of toxicity. Monitor levels. | Moderate |
| Ampicillin / Amoxicillin | Increased incidence of skin rash. | Moderate |
| Cyclophosphamide | Potential increased risk of bone marrow suppression. | Moderate |
| Chlorpropamide | Increased risk of hypoglycemia. | Moderate |
| Diuretics (Thiazides, Furosemide) | May increase serum urate levels, potentially reducing allopurinol efficacy. Also may increase risk of allopurinol hypersensitivity. | Moderate |
| ACE Inhibitors (e.g., Captopril) | May increase risk of hypersensitivity reactions. | Moderate |
Same composition (Allopurinol (300mg)), different brands: