Thiopurine methyl-transferase activity and azathioprine metabolite concentrations do not predict clinical outcome in thiopurine-treated inflammatory bowel disease patients.
ABSTRACT Low thiopurine-methyl-transferase (TPMT) activity and high 6-thioguanine-nucleotide (6TGN) concentrations have been linked to therapeutic success in inflammatory bowel disease patients treated with thiopurines; however, this has not been implemented in clinical practice.
To identify a therapeutic threshold value for TPMT or 6TGN concentrations, and their capability to predict treatment safety and efficacy.
Prospective multicentre study including steroid-resistant/dependent patients starting thiopurines. The TPMT activity was determined at inclusion (>5 U/mL required). Azathioprine metabolites [6TGN, 6-methyl-mercaptopurine ribonucleotides (6MMP), and 6TGN/6MMP and 6TGN/TPMT ratios] were periodically monitored during steroid tapering and after withdrawal for 6 months or until a new flare occurred.
A total of 113 patients were analysed (62% clinical response). Areas under the receiver operating characteristic (ROC) curve (AUC) relating clinical response and metabolite levels at 2, 4 and 6 months after steroid withdrawal were less than 0.7. The AUCs relating final response and initial TPMT activity or metabolite concentrations at 2, 4, 8 and 16 weeks after starting thiopurines were less than 0.7. No cut-off point with worthwhile sensitivity/specificity was found. Eight (7%) patients developed thiopurine-related toxicity that could not be linked to TPMT activity or 6TGN levels.
Our results do not support determination of TPMT activity or 6TGN concentrations to predict treatment outcome, and no useful serum metabolites threshold value to adjust the drug's dose was identified.
- SourceAvailable from: Frank Hoentjen[show abstract] [hide abstract]
ABSTRACT: Thiopurine therapy effectively maintains remission in inflammatory bowel disease. However, many patients are unable to achieve optimum benefits from azathioprine or 6-mercaptopurine because of undesirable metabolism related to high thiopurine methyltransferase (TPMT) activity characterized by hepatic transaminitis secondary to increased 6-methylmercaptopurine (6-MMP) production and reduced levels of therapeutic 6-thioguanine nucleotide (6-TGN). Allopurinol can optimize this skewed metabolism. We discuss two brothers who were both diagnosed with ulcerative colitis (UC). Their disease remained active despite oral and topical mesalamines. Steroids followed by 6-mercaptopurine (MP) were unsuccessfully introduced for both patients and both were found to have high 6-MMP and low 6-TGN levels, despite normal TMPT enzyme activity, accompanied by transaminitis. Allopurinol was introduced in combination with MP dose reduction. For both brothers addition of allopurinol was associated with successful remission and optimized MP metabolites. These siblings with active UC illustrate that skewed thiopurine metabolism may occur despite normal TPMT enzyme activity and can lead to adverse events in the absence of disease control. We confirm previous data showing that addition of allopurinol can reverse this skewed metabolism, and reduce both hepatotoxicity and disease activity, but we now also introduce the concept of a family history of preferential MP metabolism as a clue to effective management for other family members.Digestive Diseases and Sciences 12/2011; 57(1):250-3. · 2.26 Impact Factor
- Clinical Pharmacology & Therapeutics 01/2013; · 6.85 Impact Factor