Dissociated Antidepressant and Analgesic Effects of Intravenous Ketamine in Patients with Chronic Pain

Abstract

Objective: Recent studies about low-dose ketamine therapy have found significant improvement of depressive symptoms within a few hours or days. This study was designed to investigate the effect of ketamine on mood in patients with chronic pain.

Methods: Forty subjects with chronic pain were recruited from the pain clinic of the Ajou University Hospital. The Beck Depression Inventory was used to evaluate mood in each patient, and then the patients received ketamine hydrochloride (1.2 mg/kg, average) intravenously over the course of 1 hour. Visual Analogue Scale (VAS) for depression, anxiety, and pain were completed by the subjects just before and 3 hours after ketamine infusion.

Results: VAS scores for depression, anxiety, and pain were significantly decreased after ketamine infusion. VAS for depression, anxiety, and pain showed significant correlation with each other before ketamine infusion; however, correlations of the VAS scores for pain with the other two visual scale measures were absent at post-ketamine administration while the correlation between depression and anxiety following ketamine infusion was maintained.

Conclusion: To our knowledge, this is the first report about the antidepressant effect of intravenous ketamine, which is separated from its analgesic effect in patients with chronic pain. This result raises the possibility that the antidepressant effect of ketamine is generated by a mechanism different from that of the analgesic effect in human.