Prediction of 6-thioguanine nucleotides levels in Japanese patients with inflammatory bowel diseases during long-term thiopurine administration

Background. The monitoring of 6-thioguanine nucleotides (6-TGN) levels is warranted during thiopurine therapy for patients with inflammatory bowel diseases. Aims. The aim of this study was to elucidate the parameters that can predict the 6-TGN levels among Japanese patients with inflammatory bowel diseases undergoing thiopurine therapy. Material and methods. The 6-TGN levels were measured in 54 patients with inflammatory bowel diseases (32 with ulcerative colitis and 22 with Crohn's disease), who had been administered azathioprine or 6-mercaptopurine for more than 90 days. Possible correlations between the hematologic parameters and 6-TGN levels were investigated. The clinical and hematologic variables were evaluated to determine the 6-TGN levels of less than or over 235 pmol/8 × 10⁸ RBCs. Results. The 6-TGN levels correlated significantly with changes in the mean corpuscular volume (R 0.423, p 0.001) and the lymphocyte counts (R-0.280, p 0.04). A multivariate analysis revealed changes in the mean corpuscular volume (OR: 1.22, 95% CI: 1.071.40) and hemoglobin levels (OR: 0.59, 95% CI: 0.350.99) to be factors predictive of the 6-TGN levels. An increase in the mean corpuscular volume of 3.5 fl was determined to be the most preferable cut-off value to distinguish patients with 6-TGN ≥ 235 pmol/8 × 10⁸ RBCs from those with a lower concentration. Conclusions. Changes in the mean corpuscular volume are considered to be predictive of the 6-TGN levels in patients with inflammatory bowel diseases receiving thiopurine therapy.