A single low-dose infusion of ketamine (0.5 mg/kg) briefly reduces hopelessness and later lowers suicidal ideation in people with treatment-resistant depression and strong suicidal thoughts. In a randomized trial of 84 patients, those receiving ketamine showed significantly less hopelessness four hours after infusion compared with those receiving a control drug (midazolam). Two days after infusion, the ketamine group had more positive and fewer negative suicidal thoughts. The early drop in hopelessness predicted the later antisuicidal effect. The antihopelessness effect lasted only about four hours, while the antisuicidal effect appeared on the second day.
Low-grade inflammation (LGI) is linked to poor response to standard antidepressants, but its role in ketamine treatment for treatment-resistant depression (TRD) was unclear. In 167 patients with TRD, 46 had LGI (C-reactive protein ≥3 mg/L) and 121 did not. A single low-dose ketamine infusion improved depressive symptoms only in patients without LGI, showing no significant antidepressant effect in those with LGI. However, ketamine reduced suicidal thoughts in both groups. The placebo response was notably greater in patients with LGI, which may explain the lack of observed ketamine effect in that group. Further research is needed to confirm these findings.
A combination of clinical markers better predicts which patients with treatment-resistant depression and suicidal thoughts will respond rapidly and durably to a single low-dose ketamine infusion than any single marker alone. The markers include mild or moderate depression severity, a shorter current episode, no more than four prior antidepressant failures, low or moderate current suicide risk, and a history of suicide attempts. The analysis of 67 patients from previous trials used a decision-tree model to identify these predictors. Clinicians can use these findings to select patients most likely to benefit, though further confirmation is needed.