Randomized clinical trials (RCTs) evaluate the efficacy of treatments in selected groups of patients defined by strict inclusion criteria. The value of these trials in predicting therapeutic effectiveness in “real world” patients is limited. This observational cohort study was designed to complement the knowledge obtained in RCTs by evaluating the effectiveness of tumor necrosis factor (TNF) inhibitors in patients with rheumatoid arthritis (RA) according to their eligibility for the major trials.


Using the data from the German biologics register Rheumatoid Arthritis Observation of Biologic Therapy (RABBIT [in German]), we investigated how many of the RA patients who were treated with a TNF inhibitor (infliximab, etanercept, or adalimumab) would have been eligible for the major clinical trials that led to approval of the drugs. In addition, therapeutic effectiveness was compared in the eligible and ineligible patients using the American College of Rheumatology 20% (ACR20) and 50% (ACR50) improvement response criteria.


Only 21–33% of the patients in the RABBIT register would have been eligible for the major trials. In these patients, the ACR20 and ACR50 improvement responses, indicating therapeutic effectiveness, were comparable with the response rates in the published trials. ACR response rates were lower in those patients considered ineligible for the trials; however, absolute improvement was similar to that in eligible patients. Ineligible patients had lower baseline disease activity, more comorbidity, and lower functional status.


RCT cohorts reflect only a minor proportion of the patients treated with biologic agents in routine care. In the clinic setting, the indications for treatment with biologic agents are not identical to the inclusion criteria for trials. Despite the smaller relative improvement achieved in these patients with longstanding, severe RA who would not fulfill the inclusion criteria of a major trial, the majority of such patients would nevertheless benefit from biologic therapy.