Generic
Allopurinol
12 brands available in the market
At a glance
Allopurinol is a xanthine oxidase inhibitor used to prevent and treat gout. It lowers blood uric acid levels and prevents uric acid crystal formation in joints and kidneys.
Description
Allopurinol is a xanthine oxidase inhibitor used orally to reduce uric acid production. It inhibits the enzyme xanthine oxidase, which is responsible for converting hypoxanthine to xanthine and xanthine to uric acid (the end product of purine metabolism). This reduces blood uric acid levels and alleviates gout symptoms.
Indications
Gouty arthritis, skin tophi, nephrolithiasis (where urate/uric acid deposition has occurred); 2,8-dihydroxyadenine (2,8-DHA) renal stones; recurrent mixed calcium oxalate renal stones with hyperuricosuria.
Therapeutic class
Drugs used in Gout
Pharmacological class
Xanthine Oxidase Inhibitor
Pharmacology
Allopurinol is a xanthine oxidase inhibitor that acts on purine catabolism. It inhibits the enzyme xanthine oxidase, which is responsible for the conversion of hypoxanthine to xanthine and xanthine to uric acid. Approximately 90% is absorbed from the GI tract. Peak plasma levels occur at 1.5-4.5 hours. Plasma half-life is approximately 1-2 hours. Approximately 20% is excreted in feces.
Mechanism of action
Allopurinol inhibits xanthine oxidase enzyme, blocking the conversion of hypoxanthine to xanthine and xanthine to uric acid, thereby reducing uric acid production and alleviating gout symptoms.
Dosage
Adults:
- Mild: 100-200 mg/day
- Moderate: 300-600 mg/day
- Severe: 700-900 mg/day
- Starting dose: 100 mg/day (to reduce side effect risk)
Children (under 15 years): 10-20 mg/kg/day (max 400 mg/day)
Elderly: Lowest effective dose
Renal impairment: Severe insufficiency: <100 mg/day or longer intervals
Administration
Take with or immediately after food (to reduce stomach upset). Swallow tablet whole, do not chew. Drink adequate fluids (2-3 litres) daily.
Missed dose
If you miss a dose, take it as soon as you remember. If it is almost time for your next dose, skip the missed dose and continue with your regular schedule. Do not double the dose.
Side effects
Common side effects: Skin rash, diarrhea, nausea, vomiting, gastrointestinal discomfort
Rare: Malaise, headache, dizziness, vertigo, drowsiness, visual and taste disturbances, hypertension, alopecia, hepatotoxicity, neuropathy, gynecomastia, blood disorders
Serious allergy: Discontinue immediately if rash appears
Precautions & warnings
- Discontinue immediately if skin rash or signs of allergy appear
- Reduce dose in hepatic or renal impairment
- Use during pregnancy only when no safer alternative exists
- Caution during lactation
- Avoid alcohol (may trigger gout flare)
- Caution while driving (may cause drowsiness, dizziness)
Contraindications
Hypersensitivity to allopurinol.
Drug interactions
- 6-Mercaptopurine or Azathioprine: Reduce dose to 25% (xanthine oxidase inhibition prolongs activity)
- Vidarabine: Half-life may be increased (caution required)
- Theophylline: Monitor levels
- Ampicillin or Amoxicillin: Increased skin rash frequency
- Cyclosporine: Plasma concentration may increase
Food interactions
Caution advised with alcohol consumption (may trigger gout flare).
Use in pregnancy
Inadequate evidence of safety in human pregnancy. Use only when no safer alternative exists and disease carries risk to mother or unborn child.
Pregnancy Category: C — always consult a doctor before taking during pregnancy.
Use in lactation
Unknown effects on breastfed baby. Use with caution.
Pediatric use
Rarely indicated in children (under 15 years) except in malignant conditions and Lesch-Nyhan syndrome.
Geriatric use
Use lowest effective dose due to lack of specific data.
Renal / hepatic impairment
Renal impairment: Severe insufficiency: <100 mg/day or longer intervals. Hepatic impairment: Caution required; dose reduction may be needed.
Overdose effects
Ingestion of up to 20g may cause nausea, vomiting, diarrhea, and dizziness. Maintain adequate hydration. Hemodialysis may be used if necessary.
Storage conditions
Store below 30°C, protected from light and moisture. Keep out of reach of children.
Chemical structure
C₅H₄N₄O