OBJECTIVES: To determine health care costs of patients with rheumatoid arthritis (RA) from a single health plan who switch first- and second-line biologic disease-modifying antirheumatic drug (bDMARD) therapy. METHODS: This observational, retrospective analysis utilized administrative claims from a large, commercial health plan database containing insured beneficiaries between January 1, 2006 and December 31, 2010. The first-line population consisted of patients with RA, newly initiated on abatacept, etanercept, infliximab or adalimumab, with 12 months of continuous follow-up. A new second-line patient cohort was defined as those initiating a bDMARD with evidence of a different bDMARD up to 2 years prior to index date. Switching was defined as a different bDMARD claim within a 200% gap in days supply from the previous bDMARD claim. The days supply for bDMARDs was imputed based on the product label. Among switchers, the post-index period was divided into post-initiation pre-switch and post-switch periods. All post-index costs were monthly and calculated only for the time the patient was on a bDMARD. Bivariate and multivariate statistical analyses were conducted to determine costs of bDMARD switchers versus non-switchers.  RESULTS: Patients who switched first-line bDMARD therapy had higher baseline monthly health care costs than non-switchers ($2417 vs. $2081; p<0.001). Post-index, first-line switchers had significantly higher costs after switch than non-switchers ($6081 vs. $4415), as did second-line switchers ($8376 v.s $5625). After controlling for potential confounders, post-switching costs were increased by 35% (least squares [LS] mean $5693 vs. $4224; p<0.001) for first-line switchers and by 46% (LS mean $7799 vs. $5348; p<0.001) for second-line switchers, versus non-switchers.   CONCLUSIONS: Compared with non-switchers, health care costs are significantly higher for both first- and second-line switchers following switch. These findings reinforce the importance of understanding the implications associated with switching bDMARD therapy.