Objective: The objective of this study was to quantify the value of early suppression of high-sensitivity C-reactive protein (hsCRP) levels as a biomarker of the protective role of canakinumab against future gout flares.
Methods: We conducted a post hoc causal mediation analysis of the Canakinumab Anti-Inflammatory Thrombosis Outcome Study for gout flares. The 3-month change in the log hsCRP level was the mediator of interest. We used linear regression for the hsCRP level mediator and Cox or Weibull regression for gout-flare outcomes, combining them in causal mediation analysis. We examined the cohort overall, as well as stratified by prevalent gout at baseline.
Results: We analyzed 9,221 patients without prevalent gout and 747 with prevalent gout. The Cox regression hazard ratio (HR) for a gout flare was 0.50 (95% confidence interval [95% CI] 0.37-0.68) comparing canakinumab with placebo, of which 6% was explained by the mediated effect through hsCRP level reduction in the first 3 months. In the prevalent-gout subgroup, the HR was 0.58 (95% CI 0.36-0.95), of which 31% was explained by the mediated effect through hsCRP level reduction. The Weibull analysis gave a proportion-mediated estimate of 47%. The indirect effect via hsCRP level reductions was unclear in the subgroup without prevalent gout.
Conclusion: The first 3-month reduction in hsCRP level was not a good biomarker for canakinumab's protective effect on future gout flares in the overall cohort. Among patients with prevalent gout, there may be a potential role for early hsCRP level reduction as a biomarker for interleukin-1β inhibitors' future gout-flare benefit.
© 2021 American College of Rheumatology.