Exploring associations of 6-thioguanine nucleotide levels and other predictive factors with therapeutic response to azathioprine in pediatric patients with IBD using multilevel analysis.

BACKGROUND: Metabolite monitoring and response predictors to azathioprine (AZA) in pediatric inflammatory bowel disease (IBD) are debatable. In an attempt to optimize thiopurine therapy and understand the mechanism of action of thiopurines, we correlated metabolites and other factors with AZA efficacy in children with IBD. METHODS: Data from 86 children with IBD with 440 metabolite measurements were retrospectively analyzed using multilevel logistic regression analyses. A therapeutic response was defined as a pediatric Crohn's disease activity index ≤10 for Crohn's disease or a pediatric ulcerative colitis activity index ≤10 for ulcerative colitis without any treatment with steroids, antitumor necrosis factor, other immunomodulators, or exclusive enteral nutrition. RESULTS: The 6-thioguanine nucleotide levels >250 pmol per 8 × 10 red blood cells correlated with a higher response (odds ratio, 4.14; 95% confidence interval, 1.49-11.46, P = 0.007), whereas 6-methyl-mercaptopurine and 6-methyl-mercaptopurine:6-thioguanine nucleotide ratio showed no correlation. Other novel response predictors in children with IBD were relative leukopenia (odds ratio, 14.01; 95% confidence interval, 3.77-52.10; P < 0.001) and the absence of lymphopenia (odds ratio, 3.71; 95% confidence interval, 1.26-10.89; P = 0.017). Lower thiopurine methyltransferase activity (P = 0.015), lower platelet count (P = 0.020), and higher aspartate aminotransferase level (P = 0.009) also predicted therapeutic response. Age, gender, patient adherence, the duration of AZA therapy, IBD type, erythrocyte count, and erythrocyte sedimentation rate did not predict efficacy. The high interindividual variability accounting for 57.7% of variance in therapeutic response was observed. CONCLUSIONS: The significant 6-thioguanine nucleotide level-response relationship may support metabolite monitoring to improve thiopurine efficacy in pediatric IBD. The reported response predictors may be helpful for treatment optimization in AZA-treated children with IBD, but should be proved in prospective studies.

Usefulness of thiopurine metabolites in predicting azathioprine resistance in pediatric IBD patients.

Few data on azathioprine (AZA) therapy for inflammatory bowel disease (IBD) exist for children. We evaluated whether the 6-thioguanine nucleotides (6-TGN) level predicts AZA refractoriness in children with IBD and whether children benefit an AZA dose escalation. Seventy-eight children with IBD initially treated with an AZA dose of 1.5-2.5 mg/kg/day were retrospectively included. The dose was adjusted based on the clinical status. The receiver operating characteristic curve and logistic regression were used to determine predictors for AZA resistance. Initially, 18 of 40 (45%) patients receiving a dose of <2 mg/kg/day and 11 of 38 (28.9%) patients receiving a dose of 2-2.5 mg/kg/day achieved remission. The 6-TGN level above 250 pmol/8.10(8) RBCs was associated with a higher remission rate, though non-significant. Among 35 patients with a dose escalation due to treatment failure, 12 (34.3%) achieved remission (the median 6-TGN level increased from 260 to 394 pmol/8.10(8) RBCs [P = .002]), 23 (67.6%) were AZA refractory. A 6-TGN level above 405 pmol/8.10(8) RBCs was the only predictor for AZA resistance (sensitivity 78.3%, specificity 75%, OR 10.8 [95% CI: 2.1-55.7, P = .004]). Serial metabolite monitoring is useful to identify children with IBD resistant to AZA. Children who cannot achieve remission despite a 6-TGN level above 405 pmol/8.10(8) RBCs should receive alternative therapies than dose increase.

Relationship between azathioprine dosage and thiopurine metabolites in pediatric IBD patients: identification of covariables using multilevel analysis.

BACKGROUND: Previous studies have reported no or only a very poor correlation between 6-methylmercaptopurine/6-thioguanine nucleotide (6-MeMPN/6-TGN) and azathioprine (AZA) dose in the treatment of inflammatory bowel disease (IBD). However, metabolite levels are often repeatedly measured yielding a hierarchical data structure that requires more appropriate data analysis. METHODS: This study explored the relationship between the weight-based dosage of AZA and metabolites levels in 86 pediatric IBD patients using multilevel analysis. Other covariates related to patient characteristics and treatment were evaluated. RESULTS: This is the first study to demonstrate positive correlations between AZA dose and 6-TGN and 6-MeMPN levels and 6-MeMPN/6-TGN ratio (P < 0.001) in IBD children. Other novel predictors of metabolites were reported. Younger children exhibited lower 6-TGN and 6-MeMPN levels, probably suggesting age-related differences in metabolism and/or absorption of thiopurines. Coadministration of infliximab resulted in a significant increase in 6-TGN levels (P = 0.023). Moreover, alanine aminotransferase values positively correlated with 6-MeMPN levels (P = 0.032). The duration of AZA therapy, gender, and thiopurine methyltransferase activity were associated with metabolite levels. The wide interindividual variability in metabolite levels that accounted for 67.7%, 48.6%, and 49.4% of variance in the 6-TGN and 6-MeMPN levels and the ratio, respectively, were confirmed. CONCLUSIONS: The reliable AZA dose-metabolites relationship is useful for clinicians to guide the dosing regimen to maximize clinical response and minimize side effects or to consider alternative therapies when patients have preferential production of the toxic 6-MeMPN. These results may be of potential interest for optimizing thiopurine therapy to achieve safe and efficacious AZA use in pediatric IBD patients.

Monitoring of azathioprine metabolites in pediatric patients with autoimmune hepatitis.

Azathioprine is commonly used in the treatment of autoimmune hepatitis (AIH). Few data are available on drug monitoring of azathioprine metabolites in patients with AIH, especially in pediatric patients. The purpose of this study was to investigate intracellular thiopurine metabolites in children with AIH and to assess the relevance of drug monitoring compared with the efficacy and toxicity. Data from 28 patients with AIH treated by azathioprine for at least 3 months were recorded. 6-Thioguanine nucleotides (6-TGN) and 6-methyl mercaptopurine nucleotides (6-MeMPN) concentrations and TPMT activity were determined by high-performance liquid chromatography. Blood cell counts and liver function tests were also collected and the clinical outcome was documented. A wide interindividual variability in 6-TGN and 6-MeMPN concentrations was observed with values ranging from 51 to 1966 pmol/8 x 10(8) red blood cells (RBCs) for 6-TGN and from 42 to 8189 pmol/8 x 10(8) RBCs for 6-MeMPN. A total of 61.4% of the patients achieved remission and only 32.6% of these children had 6-TGN values within the target range proposed for inflammatory bowel disease (250-450 pmol/8 x 10(8) red blood cells). No difference in metabolite concentrations was observed between children in remission and those with active disease. Azathioprine dosage was significantly related to 6-TGN and 6-MeMPN levels (r = 0.308, P < 0.001 and r = 0.405, P < 0.001, respectively). A significant negative correlation was observed between 6-TGN concentrations and erythrocyte and lymphocyte counts, whereas 6-MeMPN was not related to blood cell counts. Although leukocyte counts were not related to 6-TGN concentrations, patients with leucopenia exhibited higher 6-TGN values than those without leucopenia (median values 438 pmol/8 x 10(8) RBCs versus 405 pmol/8 x 10(8) RBCs, respectively). Thiopurine metabolite monitoring appears useful in identifying the myelotoxicity and the hepatotoxicity as a result of azathioprine with disease recurrence and to assess adherence to therapy. A further larger study will be required to confirm the optimal recommended target for thiopurine metabolites to achieve remission in patients with AIH.