Real-world outcomes of intranasal esketamine and intravenous ketamine induction therapy for treatment-resistant depression in a community clinic: a retrospective cohort study

Introduction: Intravenous (IV) ketamine and intranasal esketamine are NMDA receptor antagonists used for treatment-resistant depression (TRD). Both have demonstrated efficacy in controlled trials, but observational evidence from real-world community settings is limited.

Methods: We conducted a single-center retrospective cohort study of adults aged 18 to 65 receiving induction therapy for TRD with intranasal esketamine or IV ketamine at a community psychiatric clinic from January 1 through December 31, 2025. Patients with prior exposure to either medication or to oral ketamine derivatives were excluded. The primary outcome was change in Patient Health Questionnaire-9 (PHQ-9) score from baseline to end of induction. Secondary outcomes included response (≥50% PHQ-9 reduction), remission (final PHQ-9 ≤4), clinically meaningful improvement (≥5 PHQ-9 reduction), induction completion, and adverse events. Within-group and per-protocol analyses were exploratory.

Results: Sixty-three patients met inclusion criteria (esketamine n=37; IV ketamine n=26). Baseline PHQ-9 scores were similar (18.22±4.49 vs. 18.27±5.41; P = 0.967), as was mean change from baseline (-10.31±5.59 vs. -9.50±5.69; mean difference 0.81, 95% CI -2.12 to 3.75; P = 0.589). Response rates were 64.9% vs. 69.2% (RR 0.94, 95% CI 0.66 to 1.33; P = 0.790), remission 32.4% vs. 23.1% (RR 1.41, 95% CI 0.61 to 3.26; P = 0.573), and clinically meaningful improvement 83.8% vs 73.1% (RR 1.15, 95% CI 0.87 to 1.51; P = 0.353). Induction completion exceeded 90% in both groups; one patient per cohort discontinued from intolerable side effects, and no serious adverse events occurred. Within-group PHQ-9 reduction was large: 10.31±5.59 points (paired t[34]=10.91; P<0.001; Cohen’s d=1.84) for esketamine and 9.50±5.69 points (paired t[23]=8.18; P<0.001; Cohen’s d=1.67) for ketamine. Findings remained statistically significant and clinically large under a pre-specified baseline observation carried forward (BOCF) sensitivity analysis (Cohen’s d=1.65 and 1.45).

Conclusions: Induction therapy with intranasal esketamine and intravenous ketamine was associated with robust antidepressant effects in a community outpatient setting, consistent with prior trial data. The modest sample size limits power to detect between-group differences and increases the risk of type II error; the absence of statistically significant between-group differences should therefore not be interpreted as evidence of equivalence. Protocol asymmetry between arms (esketamine: 12 sessions over 8 weeks; IV ketamine: 6 sessions over 3 weeks) further limits direct comparison of endpoint values between groups. Practical considerations including insurance coverage, cost, and administration logistics may help guide treatment selection. Longitudinal follow-up is planned to characterize treatment durability.