To observe the efficacy and safety of S-ketamine in the treatment of major depressive disorder (MDD), and to preliminarily explore the mechanism of antidepressant and possible acute side effects of S-ketamine.

From October 2020 to December 2021, 40 patients with newly diagnosed or recurrent MDD were recruited at the Department of Clinical Psychology of Wuxi Mental Health Center, the Department of Clinical Psychology of Wuxi Hospital of traditional Chinese Medicine, and the Department of Psychiatry of Chaohu Hospital affiliated to Anhui Medical University. The subjects were randomly divided into either a study group, which was treated with S-ketamine combined with antidepressants (n=20), or a control group (n=20), which was treated with normal saline combined with antidepressants. S-ketamine was administered at 0.4 mg/kg by single injection with a micropump. The symptoms of patients were evaluated by the Montgomery-?sberg Depression Rating Scale (MADRS) before the administration of S-ketamine or normal saline and at 24 hours, 1 week, and 4 weeks after administration. The dissociative effects were evaluated by 6-item clinician administered dissociative symptom scale. Repeated measures analysis of variance was used to compare the differences in symptom scores pre- and post-treatment between the two groups. P＜0.05 was considered statistically significant.

The scores of MARDS decreased after treatment in both group, and there was a significant difference between the two groups (P＜0.05). The MARDS score of the study group was better than that of the control group at 24 hours, 1 week, and 4 weeks, among which the 24-hour difference was the most significant. Twenty-four hours after administration of S-ketamine, five patients achieved complete remission (MADRS score ≤10), five achieved remarked remission (MARDS scores decreased by ≥30% from baseline), and nine achieved partial remission.

S-ketamine is a rapid, effective, and safe new antidepressant, and single low-dose intravenous administration has a good effect.