An increase in C-reactive protein levels during antidepressant treatment predicts treatment non-response in major depressive disorder

Background One-third of patients with major depressive disorder (MDD) exhibit low-grade inflammation as reflected by C-reactive protein (CRP) concentrations > 3 mg/L. We explored whether CRP changes from baseline to week one of antidepressant treatment (ΔCRP) can serve as a marker of treatment response. Methods CRP plasma levels were measured at baseline and after the first week of treatment in 33 MDD patients and correlated with patients' Hamilton depression scale (HAM-D), while adjusting for age, gender and body mass index. The early and final antidepressant responses were defined as a > 25% and > 50% HAM-D score reduction at week one and four of treatment compared to baseline, respectively. We compared baseline and week-one CRP levels with the paired t-test within responders and non-responders separately and ΔCRP between the groups with the ANCOVA. Results Higher ΔCRP correlated with lower final ΔHAM-D scores (r = -0.5, p = 0.006). Non-responders showed higher ΔCRP – but not baseline and week one CRP – than responders (p = 0.018, Cohen's d = 1.1). A ΔCRP increase was observed in 13/16 (81%) non-responders and 7/17 (41%) responders (Fisher's exact test's p = 0.03). A ΔCRP increase combined with an early non-response was observed in 13/16 (81%) non-responders and 1/17 (6%) responders (p < 0.0001). Conclusions Rather early ΔCRP at week one than baseline CRP might be indicative of treatment response at week four, especially if combined with early ΔHAM-D. In the future, ΔCRP could be introduced into psychiatric practice to guide treatment plans.