Thiopurine methyltransferase enzyme activity determination: Patient population
Before starting AZA, the 29 patients were prospectively randomized to one of two groups. Group 1 (n=15) did not have the TPMT assay performed; they were started on AZA at 1 mg/kg/day, and the dose was titrated upwards by 50 mg every two weeks to a target dose of 2.5 mg/kg/day. Group 2 (n=14) had the TPMT assay performed before starting AZA. All 14 patients in group 2 had normal TPMT levels (greater than 9 nmol/mL red blood cells) and started AZA at the target dose of 2.5 mg/kg/day.
At randomization, all patients in both groups had a complete blood count with differential, ALT, AST, GGT and lipase levels, to ensure that they had normal values before randomization and initiation of AZA therapy. While the patients were on AZA, complete blood count with differential, ALT, AST and GGT were measured weekly for six weeks and then monthly thereafter as a safety measure. Any additional tests or health care interventions, including AZA dose adjustments and laboratory investigations, were undertaken at the discretion of the attending gastroenterologist, who was kept blinded as to the group assignment and TPMT assay results. Patients’ disease courses were followed from the time of their enrollment in the study to the study completion date.