Oxipurinol (Oxipurinol), the major active metabolite of Allopurinol, is an inhibitor of xanthine oxidase. Oxipurinol can be used to regulate blood urate levels and treat gout^[1]. IC50 & Target: Xanthine oxidoreductase^[1] In Vitro: Allopurinol is rapidly metabolized (half-life approximately 1 h) to its active metabolite oxypurinol. Oxypurinol is an inhibitor of xanthine oxidoreductase and has a considerably longer elimination half-life (approximately 23 h)^[1].