Influence of allopurinol on thiopurine associated toxicity: A retrospective population‐based cohort study

Study (n= 37,360 thiopurine users, 1077 with concomitantly allopurinol) reported a 58% reduced risk of hepatotoxicity in those concomitantly taking allopurinol (HR 0.42; 95% CI 0.30–0.60; NNT 46) but no effect on rate of myelotoxicity (HR 0.96; 95% CI 0.89–1.03).

British Journal of Clinical Pharmacology