Exposure to Azathioprine Metabolites and Clinical Outcome in Indian Patients with Crohn’s Disease

Abstract

Aim: To determine the concentration of 6-thioguanine nucleotide (6-TGN) and 6-methylmercaptopurine (6-MMP), the interpatient variability, and the relationship with disease activity in patients with Chron’s disease on long-term stable doses of azathioprine (AZA).Methods: This is a prospective, tertiary care single-center hospital study in adult Chron’s disease patients treated with AZA. The quantification of phenotypic thiopurine methyltransferase enzyme activity in red blood cells and the estimation of the concentration of 6-TGN and 6-MMP in whole blood was performed using the HPLC-UV detector method. A clinical response was categorized as remission (Harvey-Bradshaw Index [HBI] < 5) or improvement (drop from baseline of at least three points of HBI) based on HBI. Exposure to metabolite concentrations and the clinical response to AZA treatment was observed.Results: Study analysis included 30 patients who were initiated on AZA, and they were followed up with an estimation of metabolite concentrations to determine their clinical outcome. At six months, 93% of (n = 28) patients continued to be on AZA and had clinical improvement. All the patients achieved remission of Chron’s disease. Only two patients developed adverse effects such as joint pain and thrombocytopenia.Conclusion: AZA is a safe and effective therapy in managing Chron’s disease when administered after determining thiopurine methyltransferase phenotype and with dose optimization performed using therapeutic drug monitoring of 6-TGN and 6-MMP.

Keywords: Azathioprine; Crohn’s disease; TPMT phenotype; 6-TGN; 6-MMP