Efficacy and Safety of Intranasal Esketamine in Treatment-Resistant Depression in Adults: A Systematic Review

Intranasal form of esketamine, the S-enantiomer of racemic ketamine, was approved by the US FDA in 2019 for treatment-resistant depression (TRD) in adults. Since intranasal esketamine is a newly approved drug with a novel mechanism of action, much still remains unknown in regard to its use in TRD. The objective of this study is to systematically review the latest existing evidence on intranasal esketamine, and provide a better insight into its safety and efficacy in TRD in adults. PubMed, MEDLINE (through PubMed), and Google Scholar were systematically searched from 2016 to 2021, using automation tools. After removal of duplicates and screening on the basis of title/abstract, eligibility criteria were applied and quality appraisal was done independently by two reviewers. A total of 10 studies were selected for the final review which included five clinical trials (three short-term trials, one withdrawal design relapse prevention study, and one long-term study), three post hoc studies, one case/non-case study, and one review article. Out of three short-term clinical trials, only one demonstrated a statistically significant difference between treatment with esketamine plus oral antidepressant (OAD) vs placebo plus OAD. The result of the relapse prevention study showed significantly delayed relapse of depressive symptoms in esketamine plus OAD arm when compared to placebo plus OAD arm. Similarly, the result of the long-term clinical trial showed that the improvement in depressive symptoms was found to be sustained in those using esketamine. The most common adverse effects of esketamine included nausea, dizziness, dissociation, headache, vertigo, somnolence, and dysgeusia (altered sense of taste); most were mild-moderate in severity. One case/non-case study reported rare adverse effects including panic attacks, mania, ataxia, akathisia, self-harm ideation, increased loquacity (talkativeness), and autoscopy. Intranasal esketamine has shown efficacy in reducing depressive symptoms in clinical trials, but the clinical meaningfulness of the treatment effect in the real-world population still needs to be explored. Although the safety profile of esketamine appears to be favorable in most clinical trials, some serious side effects are being reported to the FDA Adverse Event Reporting System, and therefore requires further investigation. More robust clinical trials, especially long-term randomized controlled trials are needed which can help provide a better assessment on the efficacy and safety of intranasal esketamine in the treatment of TRD.