Patterns of use, dosing, and economic impact of biologic agent use in patients with rheumatoid arthritis: a retrospective cohort study

Background: Variability in dosing and costs of biologics among patients with rheumatoid arthritis ( RA) is of interest to healthcare descision-makers. We examined dosing and costs among RA patients newly treated with infliximab or etanercept under conditions of typical clinical practice. Methods: Integrated pharmacy and medical claims data were obtained from 61 U. S. health plans. RA patients newly treated with infliximab or etanercept between July 1999-June 2002 were selected. A maintenance number of infliximab vials was determined after the loading period (2-3 infusions); those with greater than or equal to 2 occurrences of an increase in vials or an interval between infusions of < 49 days were considered to have had escalated. For etanercept patients, escalation was based on >= 2 instances of increased average daily dose. Multiple logistic regression analyses were conducted to assess variables associated with dose escalation. RA-related costs at one year post-initiation also were examined; comparisons were made using generalized linear models. Results: A total of 1,548 patients were identified (n = 598 and 950 for infliximab and etanercept respectively). Infliximab recipients were somewhat older (50.5 vs. 46.6 years for etanercept). Nearly 60% of infliximab patients increased their dose at one year, compared to 18% for etanercept. Infliximab patients who escalated dose incurred a 25% increase in mean one-year costs ($20,915 vs. $16,713 for no increase; p < 0.0001). Costs among etanercept patients did not substantially differ based on dose escalation ($14,482 vs. $13,866 respectively). Conclusions: Infliximab is associated with higher rates of dose escalation relative to etanercept, which contributes to substantially higher one-year medical costs.