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Measurement of thiopurine methyltransferase activity and azathioprine metabolites in patients with inflammatory bowel disease
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  1. P W Lowry,
  2. C L Franklin,
  3. A L Weaver,
  4. M Gennett Pike,
  5. D C Mays,
  6. W J Tremaine,
  7. J J Lipsky,
  8. W J Sandborn
  1. Division of Gastroenterology and Hepatology, Division of Clinical Pharmacology, and Section of Biostatistics, Mayo Clinic, Rochester, MN, USA
  1. Dr W J Sandborn, Mayo Clinic, 200 First Street SW, Rochester, MN 55905, USA. sandborn.william{at}mayo.edu

Abstract

BACKGROUND Measurement of 6-thioguanine nucleotide concentrations may be useful for optimising treatment with azathioprine and 6-mercaptopurine.

METHODS We conducted a study of 170 patients with inflammatory bowel disease treated with azathioprine or 6-mercaptopurine to determine the relationship between 6-thioguanine nucleotide concentrations and both disease activity, as measured by the inflammatory bowel disease questionnaire (active disease <170, remission ⩾170) and leucopenia. Blood was submitted for whole blood 6-thioguanine nucleotide concentration and leucocyte count.

RESULTS Mean (SD) inflammatory bowel disease questionnaire score was 176 (32). There was no correlation between inflammatory bowel disease questionnaire scores and 6-thioguanine nucleotide concentrations (r s=−0.09, p=0.24). Median 6-thioguanine nucleotide concentrations in 56 patients with active disease and 114 patients in remission were similar (139v 131 pmol/8×108 red blood cells; p=0.26). There was no correlation between 6-thioguanine nucleotide concentrations and leucocyte counts.

CONCLUSIONS In patients with inflammatory bowel disease treated with azathioprine or 6-mercaptopurine, 6-thioguanine nucleotide concentrations did not correlate with disease activity, as measured by the inflammatory bowel disease questionnaire, or leucocyte count. These findings are discrepant with most previous studies, possibly due to selection of responding patients who tolerated the medications. A prospective, randomised, dose optimisation trial using 6-thioguanine nucleotide concentrations is warranted.

  • azathioprine
  • 6-mercaptopurine
  • thioguanine nucleotides
  • thiopurine methyltransferase
  • inflammatory bowel disease
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Footnotes

  • Abbreviations used in this paper:
    6-TGN
    6-thioguanine nucleotides
    AZA
    azathioprine
    6-MP
    6-mercaptopurine
    CD
    Crohn's disease
    UC
    ulcerative colitis
    6-MMP
    6-methylmercaptopurine
    TPMT
    thiopurine methyltransferase
    RBC
    red blood cell
    ALL
    acute lymphoblastic leukaemia
    IBD
    inflammatory bowel disease
    IBDQ
    inflammatory bowel disease questionnaire
    WBC
    white blood cell
    5-ASA
    5-aminosalicylic acid

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