title: Thiopurines in inflammatory bowel disease: pharmacogenetics, therapeutic drug monitoring and clinical recommendations.
abstract: There is a growing interest in the use of thiopurines (azathioprine, 6-mercaptopurine and 6-thioguanine) for the management of inflammatory bowel disease. The genetically controlled thiopurine (S)-methyltransferase enzyme is involved in the metabolism of these agents and is hypothesised to determine the clinical response to thiopurines. Diminished activity of this enzyme decreases the methylation of thiopurines, theoretically resulting in potential overdosing, while high thiopurine (S)-methyltransferase status leads to overproduction of toxic metabolites and ineffectiveness of azathioprine and 6-mercaptopurine. In practice, controversies exist regarding the utility of standard thiopurine (S)-methyltransferase pheno- and genotyping. Current pharmacogenetic insights suggest that another enzyme system may participate in the efficacy and toxicity of thiopurines; inosine triphosphate pyrophosphatase. Other topics discussed in this review are the utilisation of therapeutic drug monitoring and the experimental use of 6-thioguanine in the treatment of inflammatory bowel disease. 6-Thioguanine has a less genetically controlled metabolism and skips genetically determined metabolic steps. On theoretical basis, 6-thioguanine might therefore have a more predictable profile than azathioprine and 6-mercaptopurine. However, the use of 6-thioguanine has been associated with an increased risk of nodular regenerative hyperplasia of the liver and veno-occlusive disease. Further research is warranted before 6-thioguanine can be considered as a treatment option for inflammatory bowel disease.
authors.affiliation: Department of Pharmacotherapy and Pharmaceutical Care, Groningen University Institute of Drug Exploration, University of Groningen, Bloemsingel 1, 9713 BZ Groningen, The Netherlands.
authors.forename: A F Y
authors.initials: AF
authors.lastname: Al Hadithy
authors.forename: N K H
authors.initials: NK
authors.lastname: de Boer
authors.forename: L J J
authors.initials: LJ
authors.lastname: Derijks
authors.forename: J C
authors.initials: JC
authors.lastname: Escher
authors.forename: C J J
authors.initials: CJ
authors.lastname: Mulder
authors.forename: J R B J
authors.initials: JR
authors.lastname: Brouwers
mesh_terms: D000963:Antimetabolites / Q000627:therapeutic use; D001379:Azathioprine / Q000627:therapeutic use*; D005787:Gene Frequency; D005838:Genotype; D006150:Guanine Nucleotides / Q000627:therapeutic use; D006801:Humans; D015212:Inflammatory Bowel Diseases / Q000188:drug therapy* / Q000201:enzymology; D015122:Mercaptopurine / Q000627:therapeutic use*; D008780:Methyltransferases / Q000235:genetics / Q000378:metabolism; D010641:Phenotype; D017410:Practice Guidelines as Topic; D011755:Pyrophosphatases / Q000378:metabolism; D044469:Racial Groups / Q000235:genetics; D013873:Thionucleotides / Q000627:therapeutic use; D000097630:Inosine Triphosphatase
chemical_list: D000963:Antimetabolites; D001379:Azathioprine; D006150:Guanine Nucleotides; D015122:Mercaptopurine; D008780:Methyltransferases; D011755:Pyrophosphatases; D013873:Thionucleotides; D000097630:Inosine Triphosphatase; C003964:6-thioguanylic acid; C022745:thiopurine methyltransferase