Objective: To assess the impact of patient out-of-pocket (OOP) expenditures on adherence and persistence with biologics in patients with rheumatoid arthritis (RA).

Methods: An inception cohort of RA patients with pharmacy claims for etanercept or adalimumab during 2002-2004 was selected from an insurance claims database of self-insured employer health plans (n=2,285) in the US. Adherence was defined as medication possession ratio (MPR): the proportion of the 365 followup days covered by days supply. Persistence was determined using a survival analysis of therapy discontinuation during followup. Patient OOP cost was measured as the patient's coinsurance and copayments per week of therapy, and as the proportion of the total medication charges paid by the patient. Multivariate linear regression models of MPR and proportional hazards models of persistence were used to estimate the impact of cost, adjusting for insurance type and demographic and clinical variables.

Results: Mean +/- SD OOP expenditures averaged $7.84+/-$14.15 per week. Most patients (92%) paid less than $20 OOP for therapy/week. The mean +/- SD MPR was 0.52+/-0.31. Adherence significantly decreased with increased weekly OOP (coeff= -0.0035, P<0.0001) and with a higher proportion of therapy costs paid by patients (coeff= -0.8794, P<0.0001), translating into approximately 1 week of therapy lost per $5.50 increase in weekly OOP. Patients whose weekly cost exceeded $50 were more likely to discontinue than patients with lower costs (hazard ratio 1.58, P<0.001).

Conclusion: Most patients pay less than $20/week for biologics, but a small number have high OOP expenses, associated with lower medication compliance. The adverse impact of high OOP costs on adherence, persistence, and outcomes must be considered when making decisions about increasing copayments.