Thiopurine metabolite monitoring in paediatric inflammatory bowel disease

Measurement of thiopurine metabolite levels may be useful as a clinical tool to optimize thiopurine treatment of paediatric inflammatory bowel disease (IBD).

The authors evaluated correlations between 6-thioguanine nucleotide (6-TGN) and therapeutic response, metabolite levels and drug toxicity.

Fifty-six paediatric IBD patients treated with thiopurines had 326 metabolite level measurements and were retrospectively reviewed. Clinical status and laboratory parameters were compared with metabolite levels.

There was significant correlation between 6-TGN levels and therapeutic response, with higher median 6-TGN levels among patients with therapeutic response than those with non-therapeutic response (194 vs. 146 pmol/8 x 10(8) RBC; P = 0.0004). Patients with 6-TGN levels >235 pmol/8 x 10(8) RBC were more likely to achieve therapeutic response than those below the cut-off (odds ratio, 2.5; 95% CI, 1.5-4.1). Patients who developed leukopenia tended to have higher median 6-TGN levels than those without leukopenia (261 vs. 160 pmol/8 x 10(8) RBC) but the difference was not statistically significant. There was no correlation between 6-methylmercaptopurine levels and hepatotoxicity. Two patients developed acute pancreatitis. Metabolite level measurements were helpful in identifying non-compliance in nine patients.

Monitoring of thiopurine metabolite levels is useful to guide and optimize dosing, as an adjunct to clinical judgement, blood count and liver biochemistry measurements to minimize the risk of drug toxicity and to confirm non-compliance.