Usefulness of Measuring Thiopurine Metabolites in Children with Inflammatory Bowel Disease and Autoimmunological Hepatitis, Treated with Azathioprine

Table 2

Interpretation of metabolite levels (measured in pmol/ erythrocytes) and recommended approaches. TPMT: thiopurine methyltransferase; 6-MMP: 6-methylmercaptopurine; 6-TGN: 6-thioguanine.

6-TGN	6-MMP	Interpretation	Recommendation
Very low	Very low	Nonadherence	Improve adherence
Low (<230)	Normal (<5700)	Insufficient dose	Consider dose increase
Normal (230-450)	Normal (<5700)	Therapeutic optimum	Further monitoring of treatment
High (>450)	High (>5700)	Overdosing	Dose reduction
Low (<230)	High (>5700)	Hypermethylation, risk of hepatotoxicity	Consider changing treatment or adding allopurinol with low doses of AZA
High (>450)	Normal (<5700)	Potential TPMT deficiency, risk of myelotoxicity	Monitoring blood test, consider dose reduction
Normal (230-450)	High (>5700)	Hypomethylation, risk of hepatotoxicity	Monitoring liver enzymes, split or reduce the dose
>1000	Undetectable	Potential TMPT absence, lack of methylation, risk of acute toxicity	Discontinuation of treatment