L’azathioprine dans les maladies inflammatoires chroniques intestinales : impact de son métabolisme sur l’efficacité et la sécurité thérapeutique

Abstract

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 methyl transferase is the only one routinely measured by pheno- or genotyping. A decreased TPMT activity results in a potential overdosing of TP drugs leading to myelotoxicity, whereas an ultra-high activity leads to TP ineffectiveness and overproduction of methylated compounds responsible for hepatotoxicity. TPMT determination prior to TP treatment results in an individual adapted dose. Xanthine oxidase ⁄ dehydrogenase (XOD), inosine triphosphate pyrophosphatase (ITPA) and glutathion-S-transferase (GST) are other promising enzyme targets that might help to explain TP efficacy or toxicity. ITPA and GST polymorphisms might potentially be related to some TP side effects. Drug interactions are discussed and, specifically allopurinol and aminosalicylates in terms of benefits and inconvenients. XOD inhibition by allopurinol could avoid TP-related hepatotoxicity if TP and allopurinol doses are adjusted. Utilization of thiopurine metabolites, 6-thioguanine nucleotides and 6-methylmercaptopurine, is discussed, specifically, in case of thiopurine failure and recommendations are given about their interpretation and potential dose optimization. These enzymes and metabolites tests are complementary to the regular monitoring of blood cells count and liver tests which remains mandatory.(SBIM 3) -- UCL, 201