Effect of Concomitant Benzodiazepines on the Antidepressant Effects of Ketamine: Findings From the RAPID Intravenous Ketamine Study.

Ketamine is a novel and rapidly acting treatment for major depressive disorder (MDD). Benzodiazepines are commonly coprescribed with antidepressants in MDD. This study sought to examine data from a randomized clinical trial that compared a single infusion of intravenous (IV) ketamine to midazolam placebo in treatment-resistant depression ( MDD) and to assess whether the use of concomitant oral benzodiazepines differentially affected treatment response to ketamine versus midazolam. This trial ran from December 2015 to December 2016. Subjects who were taking oral benzodiazepines (n = 44) were compared to those who were not (n = 55). A significant treatment-by-benzodiazepine effect could be interpreted as a possible moderator of differential treatment response to ketamine versus midazolam. Benzodiazepine use was examined as both a binary and a continuous predictor, to assess the impact of dosage. Benzodiazepine users did not differ from non-users on the original study's primary outcome measure, score on the 6-item Hamilton Depression Rating Scale (HDRS-6), at baseline, but the former had more severe anxiety. When oral benzodiazepine use was modeled as a binary predictor, benzodiazepine use did not impact differential treatment response. However, when benzodiazepine dosage was considered, there was a significant impact of benzodiazepine use on differential treatment response. Oral benzodiazepines significantly impacted HDRS-6 ( = .018) and Clinical Global Impressions-Severity of Illness scale (CGI-S;  = .008) scores at day 1 (24 hours post treatment); effects were nonsignificant for all day 3 outcomes. Among ketamine subjects, higher doses of benzodiazepines were associated with less improvement in depression scores at day 1. Concomitant oral benzodiazepines at higher doses may attenuate the antidepressant effects of IV ketamine at day 1 but not day 3 post-infusion. ClinicalTrials.gov identifier: NCT01920555.