Thiopurine methyltransferase enzyme activity determination: Results (Part 3)
Patients in group 1 initiated a total of nine phone calls to their physicians or nurses to discuss the AZA therapy, while patients in group 2 initiated 11 such calls. Only one additional unscheduled doctor visit occurred in group 1, in a patient presenting with jaundice and hepatitis.
It is well established that 6-MP, and its prodrug AZA, are effective in the treatment of steroid-refractory IBD and in the maintenance of steroid-induced remission. What is less clear, however, is the role of TPMT activity, the key enzyme responsible for the metabolism of AZA into toxic and therapeutic metabolites, in the management of IBD. Specifically, knowing that a patient has sufficient TPMT activity (group 2 in this study) would permit a ‘step-in’ initiation of full dose AZA on day 1, whereas not knowing the TPMT activity (group 1 in this study) would, in general, necessitate a ‘step-up’ approach in dosing over several weeks. The present study thus examined whether assessment of TPMT activity before the administration of AZA (subsequently permitting either ‘step-in’ or ‘step-up’ dosing) would predict acute toxicity and, thus, allow for reduction in health care costs related to biochemical screening for, and management of, AZA-induced adverse events.