Cognitive function of patients with treatment-resistant depression after a single low dose of ketamine infusion

Background: Clinical and animal studies have reported conflicting results regarding the effect of ketamine on cognitive function, although increasing evidence supports a rapid and sustained antidepressant effect of a subanesthetic dose of ketamine infusion for patients with treatment-resistant depression (TRD). However, the cognitive function before and after ketamine infusion was rarely investigated in patients with TRD. Methods: A total of 71 adult patients with TRD were enrolled and randomized to 0.5-mg/kg ketamine, 0.2-mg/ kg ketamine, or normal saline infusion groups. Depressive symptoms were measured using the Hamilton Depression Rating Scale at baseline and at different time points post ketamine infusion. Cognitive function was evaluated using working memory and go/no-go tasks at baseline, Day 3, and Day 14 post ketamine infusion. Results: A single low dose of ketamine infusion did not impair the cognitive function of patients with TRD. The paired t test revealed that patients with TRD receiving 0.5 mg/kg of ketamine infusion exhibited a slight improvement in sustained attention and response control measured using the go/no-go task at Day 14 post ketamine infusion. A significant association was also observed between depressive symptoms and cognitive function changes at Day 3 in the 0.5-mg/kg ketamine infusion group. Discussion: A 0.5 mg/kg dose of ketamine infusion was not harmful, but slightly beneficial, for the cognitive function of patients with TRD. Additional studies are necessary to elucidate the effects of repeated ketamine infusion on cognitive function.