Reduction in serum levels of substance P in patients with rheumatoid arthritis by etanercept, a tumor necrosis factor inhibitor.

We determined the effects of etanercept on the serum concentrations of neuropeptides in RA patients. In a total of 11 patients who had been injected with etanercept, the serum levels of substance P, calcitonin gene-related peptide (CGRP), and gastrin-releasing peptide (GRP) were analyzed. Average levels of serum substance P were significantly reduced from 1.53 to 0.62 ng/ml after the injection of etanercept. In the CGRP and GRP analyses, these average levels dropped from 1.57 and 0.51 ng/ml to 0.44 and 0.04 ng/ml, respectively. Etanercept appears to decrease substance P levels with an improvement in disease activities.