Objective: To examine treatment compliance and dosage administration associated with infliximab, etanercept, and methotrexate therapy for rheumatoid arthritis (RA).
Study design: Retrospective analysis using administrative and claims data from a large US health plan.
Patients and methods: Patients were Medicare or commercial enrollees in a health plan with a pharmacy benefit and had a diagnosis of RA. The first (index) claim for infliximab, etanercept, or methotrexate occurred between July 1, 1998, and December 31, 2000. Continuous enrollment in the plan was required from 182 days before to 365 days after the index claim. Treatment groups were compared according to compliance (defined as the actual number of therapy administrations or filled prescriptions divided by the expected number) and changes in dosage administration over time. The costs of infliximab therapy also were explored.
Results: A total of 2662 patients (infliximab = 141; etanercept = 853; and methotrexate = 1668) were included in the analyses. Infliximab patients were older and more likely to have a Medicare benefit. In addition, infliximab patients had more comorbidities and had greater medical costs preceding the index claim. Compliance with at least 80% of the expected dosages was significantly lower for etanercept (odds ratio [OR] 0.462; 95% confidence interval [CI] 0.290-0.736) and methotrexate (OR 0.385; 95% CI 0.245-0.604) patients than infliximab patients. Methotrexate patients had the largest dosage increases (61.6%), followed by infliximab (37.4%) and etanercept (7.4%) patients. Assuming 6.5 dosages per year, the annual cost of infliximab was dollars 10446 to dollars 12363, or dollars 1887 to dollars 1902 per administration, depending on site of service.
Conclusions: Compliance is higher with infliximab compared with etanercept or methotrexate; whereas, fewer etanercept patients change dosages. The cost of infliximab was lower than expected based on previous predictions, even with a 37% increase in dosage.