Clinical data gap between phase III clinical trials (pre-marketing) and phase IV (post-marketing) studies: evaluation of etanercept in rheumatoid arthritis.

BACKGROUND: There are fundamental differences in design between phase III clinical trials and phase IV post-marketing studies that involve patient characteristics, the clinical setting (environment) and the manner of drug use. As well, many phase IV studies are extensions of randomized clinical trials (RCTs) and suffer from selection bias. OBJECTIVE: To determine if the data obtained from RCTs of etanercept (Enbrel) in the treatment of …