title: The utility of thiopurine methyltransferase enzyme testing in inflammatory bowel disease.
abstract: OBJECTIVE
  To assess the levels of red blood cell thiopurine methyltransferase (TPMT) in subjects with inflammatory bowel disease (IBD) and to determine how these levels impacted thiopurine dosing and leukopenia over the first six months of therapy.
  
  
  METHODS
  A retrospective chart review was performed on all adult IBD patients (n=423, 88.2% Caucasian) who had TPMT levels measured by 11 participating gastroenterologists in Manitoba between 2008 and 2010. In addition to descriptive data, white blood cell count, dose and reason for discontinuation were analyzed for the first six months of therapy. Patients receiving ≥2.0 mg/kg of azathioprine (AZA) or ≥1.0 mg/kg of 6-mercapatopurine were considered to be 'substantially' dosed.
  
  
  RESULTS
  Of the 423 patients, 8.3% had intermediate levels and 93.4% had normal levels of TPMT. Only one subject had a low level. A total of 216 patients had sufficient data to be included for full analysis. Patients with intermediate TPMT levels were generally started at lower doses of thiopurine than patients with normal TPMT levels (mean [± SD] 1.0±0.6 mg/kg versus 1.8±0.5 mg/kg). Of the subjects with normal TPMT levels, only 37.8% were dosed with ≥2.0 mg/kg of AZA. Each month, approximately 5% of subjects were leukopenic. These subjects received a mean overall AZA dose of 1.9±0.3 mg/kg and had a mean white blood cell count of 3.8±0.4×10(9)/L.
  
  
  CONCLUSIONS
  Normal TPMT levels did not prevent the development of leukopenia, although life-threatening leukopenia was rare. Physicians are not using TPMT levels to substantially dose thiopurines at the outset, which may limit the speed at which adequate doses are reached to facilitate remission.
authors: Department of Internal Medicine, University of Manitoba, Winnipeg, Manitoba.
authors: Laura
authors: L
authors: Chisick
authors: Curtis
authors: C
authors: Oleschuk
authors: Charles N
authors: CN
authors: Bernstein
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001379:Azathioprine / Q000008:administration & dosage / Q000009:adverse effects / Q000627:therapeutic use; D003093:Colitis, Ulcerative / Q000188:drug therapy*; D003424:Crohn Disease / Q000188:drug therapy*; D004305:Dose-Response Relationship, Drug; D005260:Female; D006801:Humans; D007166:Immunosuppressive Agents / Q000008:administration & dosage / Q000009:adverse effects / Q000627:therapeutic use*; D007970:Leukopenia / Q000453:epidemiology / Q000209:etiology; D008297:Male; D008350:Manitoba; D015122:Mercaptopurine / Q000008:administration & dosage / Q000009:adverse effects / Q000627:therapeutic use; D008780:Methyltransferases / Q000378:metabolism*; D008875:Middle Aged; D012189:Retrospective Studies; D055815:Young Adult
chemical_list: D007166:Immunosuppressive Agents; D015122:Mercaptopurine; D008780:Methyltransferases; C022745:thiopurine methyltransferase; D001379:Azathioprine
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