OBJECTIVES:Biological treatments have been promising advances for individuals with rheumatoid arthritis (RA). Poor adherence and treatment discontinuation, however, may undermine therapeutic benefits and raise concerns given the high costs of these agents. Our aim was to perform a systematic review of the methods used to measure adherence to biologics and to identify previously reported biologic adherence rates among RA patients. METHODS:A MEDLINE search was performed from 1995 to 2007 using the following search terms: adherence, compliance, discontinuation, treatment retention, RA, and biologics (e.g. infliximab, etanercept and adalimumab). Additional studies were obtained from references of the identified articles. Two study investigators independently reviewed the articles to determine relevant studies and extracted information such as study objective, adherence measure, mode of measurement, and main findings in a standardized form. RESULTS:Seven of 508 articles met the inclusion criteria. Adherence was measured through prospective cohort studies (N=3), retrospective analysis of registries (N=2) or claims databases (N=2). Five of the seven studies were based in Europe and the remainder in the U.S. Adherence measures reported included medication possession ratios ([MPR], N=2) and discontinuation rates based on physician interviews (N=4) or patient self-reports (N=1). Of studies reporting MPRs, 50% to 80% of patients had a MPR≥0.80 during the course of therapy. Studies measuring discontinuation found the percentage of patients continuing therapy to range from 45% to 79% after one year of monotherapy. Adherence rates decreased in subsequent years of treatment. Combination with methotrexate or other oral RA drugs was associated with higher (N=2) and lower (N=2) adherence rates. CONCLUSIONS:Few studies have measured adherence to biologics among RA patients; however, most find adherence to such agents is suboptimal. Methods of adherence measurement varied greatly across studies. Standardized methods to measure and track adherence to biologics are needed as their use continues to increase.