Etanercept, a novel drug for the treatment of patients with severe, active rheumatoid arthritis.

The US adult rheumatoid arthritis (RA) population numbers approximately 2.1 million, with a greater proportion of cases in women. RA is a disease of the immune system that has no known cure, and current drugs do not affect the underlying cause. The side effects such drugs produce limit their usefulness, and many patients stop responding to these treatments over time. Etanercept, a biologic inflammation modulator, is a novel human recombinant version of the soluble p75 tumor necrosis factor (TNF) receptor that is linked to the Fc receptor of human immunoglobulin G subclass 1. It acts as a competitive inhibitor of the binding of TNF-alpha to cell-surface TNF receptors and thereby inhibits TNF-alpha-induced proinflammatory activity in the joints of RA patients. Etanercept acts as a cytokine "carrier" and TNF-alpha antagonist, rendering TNF-alpha biologically inactive, even though prolonging its half-life. In Phase I, II, and III clinical studies in patients with active, severe RA who had not responded to disease-modifying antirheumatic drug (DMARD) therapy, etanercept treatment decreased disease activity, increased functional activity, and improved health-related quality of life. In a recent 12-month continuation of an earlier 6-month study, 105 patients who received etanercept 25 mg subcutaneously twice weekly demonstrated rapid and sustained improvements in disease activity. The US Food and Drug Administration has approved etanercept for marketing for the treatment of moderately to severely active RA in patients who have not responded adequately to other DMARDs.