Increase in IL-6 levels among major depressive disorder patients after a 6-week treatment with duloxetine 60 mg/day: a preliminary observation

Background: Immune modifications, including changes in interleukin (IL)-6 levels, have often been observed in major depressive disorder (MDD) during treatment with selective serotonin reuptake inhibitors (SSRIs) or the serotonin norepinephrine reuptake inhibitor (SNRI) venlafaxine. Nevertheless, no equivalent observation for the SNRI duloxetine has been made to date. Method: Sixteen patients diagnosed with MDD and an actual major depressive episode according to DSM-IV criteria and 16 healthy controls entered a 6-week trial with duloxetine 60 mg/day. All subjects (n = 32) were assessed using the Hamilton Depression Rating Scale (HAM-D), the Young Mania Rating Scale (YMRS), and were monitored for IL-6 levels both at baseline and at week 6. Blood samples for IL-6 levels were evaluated by ELISA. Results: After 6 weeks of treatment, the mean total scores for HAM-D declined both in the depressed and control groups, while IL-6 modification showed an opposite trend both in depressed (12.38 +/- 19.80 to 19.73 +/- 18.94 pg/mL) and control subjects (12.25 +/- 21.12 to 17.63 +/- 20.44 pg/mL), as did YMRS (ns), although none of the subjects switched to (hypo) mania. Of note, IL-6 levels increased significantly only in the responders subgroup (n = 9; P = 0.012). Conclusion: The small sample size and weak design of this study limit the validity of our results, which should be regarded as preliminary only. Nonetheless, the trend of increasing IL-6 levels observed in responder patients treated with duloxetine should prompt further controlled, extended studies with larger samples, with the specific aim of better assessing a putative differential role of norepinephrinergic antidepressant stimulation of serotonergic reuptake inhibition in determining modifications in IL-6 levels. Ideally, more accurate replication studies may contribute to further understanding of the complex interaction of mood, antidepressant response, and the immune system.