Anti-tumor necrosis factor medications have demonstrated good efficacy in treating psoriatic arthritis (PsA). Clinical responses at the primary end point in recent clinical trials of golimumab in PsA subjects yielded lower American College of Rheumatology 20% criteria for improvement (ACR20) responses than those seen in the Infliximab Multinational Psoriatic Arthritis Controlled Trial 2 infliximab study. However, baseline C-reactive protein (CRP) levels of PsA subjects enrolled in these trials differed significantly. We hypothesized that baseline CRP levels predict the observed differing clinical response rates at the primary end point.
Combining the data from the infliximab and golimumab trials, we stratified the data by baseline CRP levels and then correlated these cohorts with response to treatment, specifically the Psoriasis Area and Severity Index and the ACR20, ACR50, and ACR70 responses.
The mean baseline CRP level in the infliximab trial was 1.9 mg/dl versus 1.4 mg/dl in the golimumab trial. Only 23% of golimumab subjects had a CRP level ≥1.7 mg/dl versus 35% of infliximab subjects (P = 0.0023). All subjects with a CRP level ≥1.7 mg/dl at baseline achieved higher ACR20, ACR50, ACR70 response rates (56%, 36%, and 18%, respectively) at the primary end point of 14 weeks in the infliximab and golimumab clinical trials than any subjects with a CRP level <1.7 mg/dl (48%, 28%, and 13%, respectively [P = 0.045, P = 0.027, and P = 0.089, respectively]).
These results demonstrate that an increased baseline CRP level predicted improved therapeutic response at the primary end point for subjects treated with both golimumab and infliximab. To allow for comparison between future drug development studies and meta-analyses, baseline CRP levels should be factored into the multivariate analysis