Monitoring 6-thioguanine nucleotide concentrations in Japanese children and adolescents with inflammatory bowel disease

6-Mercaptopurine (6-MP) and azathioprine (AZA) are widely used as maintenance therapy in children with inflammatory bowel disease (IBD). However, proper 6-thioguanine nucleotide (6-TGN) concentrations in Japanese children with IBD have not been reported.This retrospective review examines 32 ulcerative colitis (UC) patients and 19 Crohn's disease (CD) patients (12.87 ± 3.56 years) who required 6-MP or AZA to maintain disease remission. All patients were treated with 6-MP or AZA for at least 3 weeks prior to this study in addition to previous treatment. 6-MP dose, 6-TGN levels, assayed by high-performance liquid chromatography, as well as laboratory data were evaluated.Thirty-five children were successfully kept in remission with 6-MP and AZA therapy after weaning off corticosteroids. Overall, 123 measurements (59 active disease, 64 in remission) were analyzed. The mean 6-TGN concentration of the entire study population was 499.61 ± 249.35 pmol/8 × 10(8) red blood cell. The mean 6-MP dose in patients with active disease (0.910 ± 0.326 mg/kg per day) was significantly higher than for patients in remission (0.749 ± 0.225) (P = 0.0016). A significant inverse correlation was found between white blood cell counts and 6-TGN concentrations (r = 0.275, P0.002). Two patients experienced leukopenia with alopecia, and four transiently experienced increased serum levels of pancreatic enzymes, although no thiopurine S-methyl transferase mutations were confirmed.The doses of 6-MP or AZA needed to maintain remission in Japanese children with IBD are lower than those reported in Western countries. However, 6-TGN concentrations in this population are higher than previously reported.