1. It functions as a xanthine oxidase inhibitor.
  1. Purines (degradation products of amino acid and nucleic acid) are converted to xanthines and hypoxanthines, before being oxidized to uric acid.
    • Allopurinol inhibits the final step and increases the amount of xanthine and hypoxanthine, which are both more water soluble.
  2. Indications as follows:
    • Used in between acute gout attacks. Should not be used in the acute phase because it may actually precipitate an acute gout attack.
    • Used to prevent increased in uric acid following therapy of blood dyscrasias (this reduces the chance of formation of uric acid stones)
    • May also be used as an anti-protozoal drug.
  3. Adverse effects
    • Precipitate gout (use colchicine or NSAIDs as a bridge)
    • Nausea, vomiting and diarrhea
    • Bone marrow suppression.
  4. Interactions
    • May increase the activity of oral anti-coagulants by inhibiting their metabolism.
  1. Given PO
    • Well absorbed, good bioavailability.
    • It is metabolized by xanthine oxidase, but its metabolic byproduct retains the ability to further inhibit xanthine oxidase.