Allopurinol

Pharmacologic profile and clinical uses

Description/Definition

Allopurinol is a xanthine oxidase inhibitor used primarily to treat hyperuricemia and its complications, including chronic gout and uric acid nephropathy.

Mechanism of action

Xanthine Oxidase Inhibition: Allopurinol inhibits xanthine oxidase, an enzyme responsible for converting hypoxanthine and xanthine to uric acid. This decreases uric acid production.

Indications

• Chronic gout Hyperuricemia associated with malignancy.
• Calcium oxalate calculi with hyperuricosuria.

Key aspects of drug therapy management

Dosage and administration

• Typical Starting Dose: 100 mg once daily, titrated based on serum uric acid levels.
• Maintenance Dose: 200-600 mg per day, with a maximum of 800 mg per day.
• Administration: Oral, preferably after meals to minimize gastrointestinal irritation.

Side effects

• Common: Rash, gastrointestinal upset.
• Serious: Stevens-Johnson syndrome, toxic epidermal necrolysis, hypersensitivity reactions.
• Important: Monitor renal function; dose adjustments may be necessary in renal impairment.

Drug interactions

• Azathioprine and 6-Mercaptopurine: Allopurinol can increase toxicity; dose adjustment required.
• Warfarin: Enhanced anticoagulant effects; monitor INR.

Monitoring

• Renal Impairment: Dose reduction is necessary in patients with renal insufficiency to prevent accumulation and toxicity.
• Concurrent Use: Use cautiously with other medications metabolized by xanthine oxidase.
• Prognosis and Monitoring: Regular monitoring of serum uric acid levels is essential to adjust dosing. Monitor for signs of hypersensitivity, especially in patients with renal impairment.