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 >or= 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 >or= 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 dollars vs. 16,713 dollars for no increase; p < 0.0001). Costs among etanercept patients did not substantially differ based on dose escalation (14,482 dollars vs. 13,866 dollars respectively).

CONCLUSIONS

Infliximab is associated with higher rates of dose escalation relative to etanercept, which contributes to substantially higher one-year medical costs.