Sex- and Age-Stratified Differences in Antidepressant Response to Intranasal Esketamine in Treatment-Resistant Depression: A Secondary Analysis of the REAL-ESK Study

Background: Intranasal esketamine (ESK-NS) is an effective treatment for treatment-resistant depression (TRD), but whether antidepressant outcomes differ by sex and age remains insufficiently explored. Methods: This secondary analysis of the REAL-ESK study included 210 patients with TRD treated with ESK-NS in routine clinical practice and assessed at baseline (T0), one month (T1), and three months (T2). The primary outcome was change in Montgomery–Åsberg Depression Rating Scale (MADRS) scores. Repeated-measures ANOVA tested Time and Time × Sex effects, with post-hoc contrasts corrected using the Holm procedure. Response and remission at T2 were compared by sex. Exploratory analyses stratified patients by age (<65 vs. ≥65 years). Results: MADRS scores decreased markedly over time (Time: F = 340.707, p < 0.005), with a significant Time × Sex interaction (F = 3.283, p = 0.043). At T2, men had lower MADRS scores than women (Δ = −3.95, Holm p = 0.023) and showed higher response and remission rates. In age-stratified analyses, sex differences were small and non-significant among participants <65 years. In those ≥65 years, the T2 contrast numerically favored men, but did not reach significance in post-hoc Holm’s correction and should be considered exploratory. Safety outcomes and discontinuation rates were broadly comparable between sexes. Conclusions: ESK-NS was associated with substantial antidepressant improvement in a real-world TRD cohort. Findings suggest a modest overall male advantage, while age-stratified patterns remain exploratory. Endocrine, vascular, inflammatory, pharmacokinetic, and treatment-context factors should be investigated in prospective studies.