Objective: To determine the safety and efficacy of recombinant soluble human interleukin-1 receptor type I (rHuIL-1RI) administered subcutaneously in patients with active rheumatoid arthritis (RA).
Methods: Twenty-three patients with active RA (>5 swollen joints) were enrolled into a randomized, double-blind, 2-center study. Patients received subcutaneous doses of rHuIL-1RI or placebo for 28 consecutive days. Patients were treated with 125, 250, 500, or 1,000 micrograms/m2/day of rHuIL-1RI. Physical examinations and laboratory assessments were performed at baseline (day 1), and 8, 15, 22, 29, 43, and 57 days after the start of the study. Analysis of peripheral blood by flow cytometry was performed on days 1 and 29 to determine the effects of rHuIL-1RI on the distribution and phenotypic characteristics of circulating inflammatory cells.
Results: Four of 8 patients who received rHuIL-1RI at 1,000 micrograms/m2/day demonstrated improvement in at least 1 of 8 individual measures of disease activity; however, only 1 of these 4 patients experienced clinically relevant improvement as defined by predetermined criteria. None of the patients treated with smaller doses of rHuIL-1RI, and none of the placebo-treated control patients, experienced any improvement as defined by the predetermined criteria. Monocyte cell surface IL-1alpha was significantly reduced following treatment with rHuIL-1RI at each dosage. Administration of rHuIL-1RI was stopped prematurely because of dose-limiting rashes in 2 patients treated with 1,000 micrograms/m2/day. No other adverse events prevented completion of the study.
Conclusion: Only 1 patient, who was treated with the highest concentration of rHuIL-1RI employed (1,000 micrograms/m2/day), demonstrated clinically relevant improvement in this phase I study on this small group of patients with active RA. Dose-limiting toxicity was also observed in 2 patients treated with this highest concentration of rHuIL-1RI. Treatment with rHuIL-1RI did result in a reduction of monocyte cell surface IL-1alpha, which indicates that the dosages of rHuIL-1RI employed were functional.