Allopurinol 100 mg Film Coated · Tablets

Allopurinol Tablets (allopurinol) is a structural analogue of the natural purine base, hypoxanthine.

Allopurinol acts on purine catabolism, without disrupting the biosynthesis of purines. It reduces the production of uric acid by inhibiting the biochemical reactions immediately preceding its formation. It is an inhibitor of xanthine oxidase, the enzyme responsible for the conversion of hypoxanthine to xanthine and of xanthine to uric acid, the end product of purine metabolism in humans. Allopurinol is metabolized to the corresponding xanthine analogue, oxypurinol (alloxanthine), which also is an inhibitor of xanthine oxidase.

Absorption — Allopurinol Tablets is approximately 90% absorbed from the gastrointestinal tract. Peak plasma levels generally occur at 1.5 hours and 4.5 hours for Allopurinol Tablets and oxipurinol respectively. After a single oral dose of 300 mg Allopurinol Tablets, maximum plasma levels of about 3 mcg/mL of Allopurinol Tablets and 6.5 mcg/mL of oxipurinol are produced.

Elimination — The half-life of allopurinol and oxipurinol are approximately 1 hour to 2 hours and 15 hours following oral dose of Allopurinol Tablets, respectively.

Metabolism — Allopurinol is metabolized to the corresponding xanthine analogue, oxypurinol (alloxanthine), which also is an inhibitor of xanthine oxidase.

Excretion — Allopurinol Tablets and its primary active metabolite, oxipurinol, are eliminated by the kidneys. Approximately 20% of the ingested Allopurinol Tablets is excreted in the feces. Oxipurinol is primarily eliminated unchanged in urine by glomerular filtration and tubular reabsorption.

Drug Interaction Studies — Capecitabine: Concomitant use with allopurinol may decrease concentration of capecitabine’s active metabolites, which may decrease capecitabine efficacy.

Cyclosporine: Concomitant use of allopurinol increases cyclosporine concentrations which may increase the risk of adverse reactions.

Mercaptopurine or Azathioprine: Allopurinol inhibits xanthine oxidase mediated metabolism of mercaptopurine and azathioprine. Concomitant use of allopurinol increases the exposure of either mercaptopurine or azathioprine which may increase the risk of their adverse reactions including myelosuppression.

Theophylline: Concomitant use of allopurinol doses greater than or equal to 600 mg/day may decrease the clearance of theophylline.

Uricosuric Agents: Uricosuric agents increase the excretion of the active allopurinol metabolite oxypurinol. Concomitant use with uricosuric agents decreases oxypurinol exposure which may reduce the inhibition of xanthine oxidase by oxypurinol and increases the urinary excretion of uric acid.

Warfarin: Allopurinol may inhibit the metabolism of warfarin, possibly enhancing its anticoagulant effect.