Allopurinol is a drug used for the treatment of gout.
It works by inhibiting xanthine oxidase, an enzyme involved in the production of uric acid. (Uric acid is the metabolite responsible for gout.)
Allopurinol can also be given with some cancer treatments that increase uric acid, as well as for kidney stones.
Allopurinol is a analog of the natural purines in the body, and is quickly metabolised to oxipurinol[?] which is also a xanthine oxidase inhibitor.
It can be given in tablet (usually 100 mg - 300 mg), or by injection. The side effects of high levels of precursors are usually very minor.
