Putting findings in perspective
Several aspects of the trial are noteworthy. First, enrolled patients were markedly depressed, and half required additional suicide precautions in addition to hospitalization. Three patients (all in the placebo group) made suicide attempts during the follow-up period, further evidence that these patients were extremely high risk. Second, the sample was significantly more racially diverse (38% black or African American) than most previous ketamine studies. Third, psychiatric hospitalization plus the initiation of standard antidepressant medication resulted in substantial improvements for many patients randomized to intranasal placebo spray. Inflated short-term placebo responses are commonly seen even in severely depressed patients, making signal detection especially challenging for new drugs. Finally, it is difficult to compare the results of this study with the few placebo-controlled trials of intravenous ketamine for patients with MDD and significant suicidal ideation, because of differences in outcomes measures, patient populations, doses, and route of administration. This study used the Suicide Ideation and Behavior Assessment Tool, a computerized, modular instrument with patient-reported and clinician-reported assessments, which was developed specifically to measure rapid changes in suicidality and awaits further validation in ongoing studies.
Limitations of this study include the absence of reported plasma esketamine levels. Is it possible that higher doses of esketamine, or a different dosing schedule, would have had resulted in greater efficacy? The 84-mg dose used in this trial recently was found to be safe and effective in patients with TRD2, and was reported to have similar plasma levels as IV esketamine 0.2 mg/kg2. This dose, in turn, corresponds to a racemic ketamine dose of approximately 0.31 mg/kg1. Future studies will need to examine the antisuicidal and antidepressant effects of the most commonly used racemic ketamine dose (0.5 mg/kg), compared with 84 mg intranasal esketamine. The twice per week dosing schedule was supported empirically from a previous study of intravenous ketamine showing that twice weekly infusions were equally effective to thrice weekly administrations7. It is unknown, however, whether even less-frequent administrations (such as once weekly) would have been more effective than twice-weekly over the 4-week, double-blind period. Finally, the authors raise the possibility of functional unblinding, which always is a concern in ketamine studies. Although the placebo solution contained a bittering agent to simulate the taste of esketamine intranasal solution, the integrity of the blind was not reported.
Conclusion
Overall, this study is a promising start. In my view, the risk to benefit ratio for this approach is acceptable, given the morbidity and mortality associated with suicidal depression. The fact that esketamine nasal spray would be administered only under the observation of a clinician in a medical setting, and not be dispensed for at-home use, is reassuring and would mitigate the potential for abuse. In the meantime, our field awaits the results of larger phase 3 studies for patients with MDD at imminent risk for suicide.
Dr. Mathew is affiliated with the Michael E. Debakey VA Medical Center, and the Menninger Department of Psychiatry and Behavioral Sciences at the Baylor College of Medicine in Houston. Over the last 12 months, he has served as a paid consultant to Alkermes and Fortress Biotech. He also has served as an investigator on clinical trials sponsored by Janssen Research and Development, the manufacturer of intranasal esketamine, and as an investigator on a trial sponsored by NeuroRx.