Usefulness of thiopurine methyltransferase and thiopurine metabolite analysis in clinical practice in patients with inflammatory bowel diseases

Thiopurines (TP) are widely used in the management of inflammatory bowel diseases. Side-effects and inefficacy are a major concern as they lead to withdrawal of the drug. Tools investigating TP metabolism are useful to avoid inadequate cessation of TP therapy. TP metabolism is complex and many enzymes are involved. Among them, Thiopurine methyltransferase (TPMT) is the only one routinely measured by pheno- or genotyping. In this review, the rationale for TPMT and thiopurine metabolites, 6-thioguanine nucleotides and 6-methylmercaptopurine, determination in clinical practice is discussed, specifically in case of thiopurine failure and recommendations are given about their interpretation and potential dose optimization of TP drugs.