One patient in group 2 developed clinical pancreatitis (lipase 2912 U/L) two weeks after starting the drug and was withdrawn. Two patients in group 2 withdrew from the study at 1 and 3.6 months because the AZA provided no therapeutic effects. Patients in group 1 withdrew at a mean of 2.7±2.8 months (range 0.4 to 8.0 months) after initiation of the drug therapy, while patients in group 2 withdrew at a mean of 1.6± 1.4 months (range 0.2 to 4.0 months). For the 13 patients still in the study at its termination, mean follow-up was 8.0±2.3 months (range 3.5 to 10.7 months).
Evaluation of all direct health care costs revealed that the costs for group 1 ($300.31 per patient) were less that those for group 2 ($348.87 per patient) (Figure 2). This increased cost in group 2 was almost fully attributable to the cost of the TPMT assay.
To determine whether TPMT assay determination affected the initiation and cost of additional laboratory and diagnostic investigations, the total number of scheduled and nonscheduled hematological and biochemical investigations and phone calls and visits to the nurse/physician were recorded. Group 1 had a significantly higher number of physician/nurse-initiated hematological and biochemical investigations than group 2 (Table 4) (P=0.013), as a consequence of physicians monitoring for side effects and toxicities. However, this translated into only a small increase in additional laboratory and diagnostic costs, $39.21 versus $37.77, group 1 versus group 2, respectively .
Figure 2) Total direct costs for groups 1 and 2. Routine costs included protocol-defined blood work every week for six weeks, then monthly thereafter for the duration of enrollment in the study. Additional costs included physician-initiated hematological blood tests, biochemical tests, radiological imaging, telephone calls to the physician/nurse and visits to the physician. Group 1: no thiopurine methyltransferase (TPMT) assay before initiation of azathioprine; Group 2: TPMT assay performed before initiation of azathioprine
TABLE 4 Summary of cost items
|Group||Protocol-defined hematological and biochemical investigations (n)||Physician-initiated hematological and biochemical Physician-initiatedinvestigations (n) abdominal ultrasound (n)||Patient-initiated phone calls (n)||Unscheduled physician visit (n)|
|Group 1||101||10* 1||9||1|
*P=0.013 relative to group 2. Group 1: No thiopurine methyltransferase assay before initiation of azathioprine; Group 2: thiopurine methyltransferase assay performed before initiation of azathioprine