The safety and efficacy of interleukin-1 receptor antagonist in the treatment of rheumatoid arthritis.

Interleukin (IL)-1 has been associated with joint inflammation and damage in rheumatoid arthritis (RA). Endogenous IL-1 receptor antagonist (IL-1Ra) may inhibit IL-1-mediated effects by binding to the IL-1 receptors. These studies were conducted to determine the efficacy and safety of human recombinant IL-1 receptor antagonist (IL-1ra) in blunting the effects of IL-1 in patients with RA. Three randomized clinical trials have been completed. First, in a 24-week, double-blind, placebo-controlled study of 472 patients with severe RA, patients were randomly placed into 4 groups: placebo or IL-1ra at 30, 75, or 150 mg/d. In a second study, 309 patients from the placebo-controlled trial enrolled in a 24-week extension study. Patients who had been receiving placebo were randomized into 1 of the 3 treatment groups. Those receiving treatment continued to receive their previous dosages. Finally, in a second double-blind, placebo-controlled study, 419 patients with RA receiving methotrexate at 12.5 to 25 mg/wk for at least 6 months were randomly placed into 1 of 6 groups: placebo or IL-1ra at 0.04, 0.1, 0.4, 1.0, or 2.0 mg/kg/d. In the first study, the primary therapeutic endpoint-an American College of Rheumatology 20% response (ACR20)-was reached by 27% of the placebo group, compared with 43% of the IL-1ra 150-mg/d group. Individual clinical responses, as well as the arrest of joint damage, were also superior in treated patients. In the second trial, 52% of the randomized patients achieved an ACR20. This was maximal (71%) in those receiving the highest treatment dosage. Of patients continuing with the same dosage, 49% maintained an ACR20 at 48 weeks. Radiologic evaluation showed that the reduced rate of cartilage degradation observed in treated patients during the first 24 weeks was maintained, and the rate of joint erosion was slowed even more significantly in the second phase of the study. In the third study, significantly more patients receiving IL-1ra at 1.0 (46%, P =.001) or 2.0 (38%, P =.007) mg/kg/d achieved an ACR20 at week 12 than those receiving placebo (19%). Similar responses were noted at week 24. IL-1ra was generally well tolerated, with injection site reaction the most frequent adverse event. No serious adverse events attributable to IL-1ra treatment were observed. These studies suggest an important role for IL-1ra as a novel therapeutic agent in the treatment of RA.