Allopurinol is a xanthine oxidase inhibitor. It blocks the conversion of hypoxanthine and xanthine to uric acid by competitively inhibiting xanthine oxidase. Allopurinol is oxidized by xanthine oxidase to oxypurinol. Both allopurinol (via competition) and oxypurinol (non-competitive inhibitor) inhibit xanthine oxidase, thereby decreasing the conversion of hypoxanthine and xanthine to uric acid. The net result is a reduction in uric acid production and thus lowers serum levels.


is indicated as prophylaxis of gout attacks and/or treatment of tophi in gout-patients with an overproduction of uric acid or nephrolithiasis. The daily dose varies from 100-600 mg orally. The dosage is adjusted after measuring serum levels of uric acid and monitoring the number of gout attacks.

Serious hypersensitivity reactions to allopurinol can occur, but are rare. Most common side effects are rash, headaches, dyspepsia and diarrhea.

Some important drug interactions to consider:

- with purine analogs (azathioprine and 6-mercaptopurine). Lower those doses with 25-50%.

- theophylline co-treatment leads to an accumulation of theophylline.


What is NOT true about allopurinol?