Allopurinol

Pharmacology of Allopurinol (Zyloric)

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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.

This note has been edited and reviewed by the pharmacy doctors on NPS team.