OBJECTIVE: Variability in dosing of biologic agents among patients with rheumatoid arthritis (RA), and associated economic impact, is of great interest to payers and providers. We examined dosing patterns for patients with RA who were newly treated with infliximab or etanercept as well as corresponding one-year costs of care. METHODS: Integrated pharmacy and medical claims data were obtained from 61 U.S. health plans. Patients with a diagnosis of RA who were newly treated with infliximab or etanercept from July 1999 to June 2002 were selected. Among infliximab patients, a maintenance number of vials was determined after the "loading period" (2-3 infusions); those with >2 occurrences of an increase in vials or an interval between infusions of < 49 days were considered to have had escalated. For etanercept patients, a maintenance dose was measured on the second prescription based on the average daily dose dispensed (in mg); those with >2 instances of increased average doses were considered to have escalated their dose. RA-related costs at one year post-initiation were examined; statistical comparisons were made using generalized linear models with a gamma distribution. RESULTS: A total of 1548 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 experienced an increase in dose at one year, compared to 18% of patients new to etanercept. Infliximab patients who experienced a dose increase had significantly higher annual RA-related costs than those with no increase ($20,915 vs. $16,713; p <0.0001). Costs among etanercept patients did not substantially differ based on dose escalation ($14,482 vs. $13,866 respectively). CONCLUSIONS: Patients new to infliximab had much higher rates of dose escalation relative to etanercept recipients. These dose increases resulted in significantly higher medical costs at one year.