Risk factors for thiopurine‐induced myelosuppression and infections in inflammatory bowel disease patients with a normal TPMT genotype

Summary Background Leucopenia is a common side effect in patients treated with thiopurines. Variants in the thiopurine S‐methyltransferase (TPMT) gene are the best‐known risk factor, but only explain up to 25% of leucopenia cases. Aim To identify the clinical risk factors for thiopurine‐induced leucopenia in patients without a common TPMT variant, and explore if these patients are at increased risk for infections. Methods Post hoc analysis of the Thiopurine response Optimisation by Pharmacogenetic testing in Inflammatory bowel disease Clinics (TOPIC) trial. For this analysis, patients without a variant in TPMT (*2, *3A or*3C) were included. Uni‐ and multivariate Cox‐proportional hazard models were used to identify risk factors for leucopenia and infections. Leucopenia was defined as a white blood cell (WBC) count