Abstract

Allopurinol (Zyloric - BW) is an isomer of hypoxanthine, and marks a new approach to the long-term treatment of gout.^{1 2} It is well established that drugs which increase uric acid excretion such as probenecid (Benemid - MSD) and sulphinpyrazone (Anturan - Geigy), although liable to precipitate acute attacks of gout at the beginning of treatment, eventually reduce the incidence of such attacks and lead to the disappearance of tophaceous deposits in the body. With these drugs the plasma levels of uric acid tend to become normal and remain so. Allopurinol produces the same effects, not by increasing uricosuria, but by inhibiting xanthine oxidase, the enzyme responsible for converting xanthine and hypoxanthine to uric acid: the solubility and renal clearance of these two substances are greater than those of uric acid, and so they are more easily excreted.