Objective To examine the effect of high baseline anxiety on response to ketamine versus midazolam (active placebo) in treatment‐resistant depression (TRD).

Methods In a multisite, double‐blind, placebo‐controlled trial, 99 subjects with TRD were randomized to one of five arms: a single dose of intravenous ketamine 0.1, 0.2, 0.5, 1.0 mg/kg, or midazolam 0.045 mg/kg. The primary outcome measure was change in the six‐item Hamilton Rating Scale for Depression (HAMD6). A linear mixed effects model was used to examine the effect of anxious depression baseline status (defined by a Hamilton Depression Rating Scale Anxiety‐Somatization score ≥7) on response to ketamine versus midazolam at 1 and 3 days postinfusion.

Results N = 45 subjects had anxious TRD, compared to N = 54 subjects without high anxiety at baseline. No statistically significant interaction effect was found between treatment group assignment (combined ketamine treatment groups versus midazolam) and anxious/nonanxious status on HAMD6 score at either days 1 or 3 postinfusion (Day 1: F(1, 84) = 0.02, P = 0.88; Day 3: F(1, 82) = 0.12, P = 0.73).