Non-response to short-term ketamine use for treatment-resistant depression.

Background: Ketamine is currently gaining attention as a rapid-acting antidepressant for treatment-resistant depression (TRD). However, many patients fail to respond, and limited data exist on predictors of non-response. This study aims to characterize the sociodemographic and clinical features associated with non-response to ketamine among TRD patients.

Methods: This is a post-hoc analysis of a naturalistic observational study, which enrolled 40 inpatients with treatment-resistant major depressive disorder and analyzed sociodemographic and clinical features in responders and non-responders stratified per Montgomery-Åsberg Depression Rating Scale (MADRS) during short-term ketamine administration (intravenous dosage: 0,5 mg/kg and orally: 2.0 or 2.5 mg/kg) that comprise over 4 weeks.

Results: In this study, 30 patients (75%) were classified as non-responders. No significant differences were detected among sociodemographic and clinical features beyond the history of substance use disorder (SUD) - only 53.3% of non-responders reported prior SUD (vs. 100%; p = 0.0075) and a lower number of psychiatric comorbidities (p = 0.0381).

Conclusion: This study highlights key characteristics of TRD non-responders to ketamine, including lower rates of SUD and fewer psychiatric comorbidities. These findings suggest that a higher burden of traditional TRD risk factors may not limit ketamine efficacy and could even enhance response compared to "pure" major depressive disorder. Identifying potential non-responders early can optimize treatment decisions, reduce ineffective exposure, and guide future research on improving TRD management.