Psychiatry · Medical Literature
Preliminary evidence that serum interleukin-6 is a candidate biomarker of response to esketamine in treatment-resistant depression.
Abstract
Interleukin-6 (IL-6) has been implicated as a potential predictor of ketamine response in treatment-resistant depression (TRD). Esketamine, the S-enantiomer of ketamine, produces rapid antidepressant effects and offers improved safety and intranasal administration. To examine whether baseline IL-6 predicts treatment response to esketamine in individuals with TRD. Fourteen adults with TRD received intranasal esketamine twice weekly for 4 weeks, followed by a tapering phase, in a 24-week open-label Phase 2 trial. Depression severity and functional disability were assessed using the Montgomery-Åsberg Depression Rating Scale (MADRS) and World Health Organization Disability Assessment Schedule at baseline, week 8, and week 24. Serum IL-6 levels were measured at the same time points. Linear mixed-effects models were used to evaluate the predictive value of IL-6. MADRS scores improved significantly over time. Higher IL-6 levels were associated with more rapid symptom reduction, whereas lower IL-6 predicted greater symptom severity and higher disability. IL-6 levels did not change significantly over the course of treatment. Baseline IL-6 may predict response to esketamine in TRD, highlighting the potential role of inflammation in treatment resistance and supporting biomarker-guided personalized interventions.
Clinical relevance
Does baseline serum interleukin-6 (IL-6) level predict antidepressant response to intranasal esketamine in adults with treatment-resistant depression (TRD)? __SNAPSHOT__ {"studyDesign":"Open-label, single-arm Phase 2 clinical trial with repeated-measures linear mixed-effects modeling","setting":"University of Udine and Friuli Centrale Health University Authority (ASUFC), Udine, Italy; academic psychiatric unit","sampleSize":"n = 14 (single arm)","population":"Adults with treatment-resistant depression (TRD); specific diagnostic criteria, prior treatment failure thresholds, comorbidity exclusions, and inflammatory status at baseline not further detailed in abstract","intervention":"Intranasal esketamine administered twice weekly for 4 weeks, followed by a tapering phase, over a 24-week total treatment period","comparator":"Not applicable (single-arm study; no placebo or active comparator group)","primaryOutcome":"Depression severity assessed by the Montgomery–Åsberg Depression Rating Scale (MADRS); functional disability assessed by the WHO Disability Assessment Schedule (WHODAS); serum IL-6 measured at baseline, week 8, and week 24","followUp":"24 weeks","fundingSource":"Not reported; lead author (Prof. Colizzi) discloses honoraria and advisory relationships with Janssen-Cilag S.p.A. (manufacturer of esketamine), Epitech Group, GW Pharma, F. Hoffmann-La Roche, and others outside this work"}
Key findings
MADRS scores improved significantly over time across the 24-week treatment course (specific effect sizes, p-values, and confidence intervals not reported in abstract). Higher baseline serum IL-6 levels were associated with more rapid symptom reduction on the MADRS, while lower baseline IL-6 was associated with greater symptom severity and higher functional disability over follow-up (quantitative regression coefficients, odds ratios, and confidence intervals not reported). Serum IL-6 levels did not change significantly from baseline to weeks 8 or 24, suggesting esketamine did not substantially modulate systemic IL-6 in this sample. No specific adverse event frequencies, NNT, or NNH data were reported in the abstract. All effect size estimates, p-values, and confidence intervals from the linear mixed-effects models are not reported in the available abstract.
Practice implications
This study provides preliminary signal that elevated baseline serum IL-6 may identify a subgroup of TRD patients more likely to respond rapidly to intranasal esketamine, lending indirect support to the hypothesis that inflammatory biology contributes to treatment resistance in depression. However, several critical limitations preclude any change in clinical practice: (1) the sample size of n=14 is insufficient to support robust inference, establish a predictive threshold, or adjust for confounders; (2) there was no control group, so observed MADRS improvement cannot be attributed solely to esketamine; (3) specific effect sizes, confidence intervals, and p-values are not reported in the abstract, preventing assessment of statistical or clinical significance; (4) IL-6 levels did not change with treatment, leaving open the mechanistic question of whether IL-6 is a true pharmacodynamic biomarker or merely a prognostic marker; (5) patients with comorbid inflammatory conditions, differences in concomitant medications, or varying metabolic states could confound IL-6 measurements; (6) this summary is based on the abstract only, and full-text review may reveal additional methodological details, covariate adjustments, and data not available here. The findings are hypothesis-generating and suitable for informing future adequately powered biomarker-stratified RCTs, but IL-6 measurement should not be used to guide esketamine prescribing decisions at this time. __LIMITATIONS__ Critically underpowered: n=14 provides insufficient statistical power to validate a predictive biomarker or detect clinically meaningful effect sizes with acceptable precision.,Single-arm, open-label design with no placebo or active comparator; MADRS improvement cannot be causally attributed to esketamine alone (regression to the mean, expectation bias, natural course).,Absence of reported quantitative statistics (effect sizes, p-values, confidence intervals) in the abstract prevents independent evaluation of the strength of the IL-6–response association.,Three-timepoint biomarker sampling (baseline, week 8, week 24) limits granularity of inflammatory trajectory data; early post-dose kinetics of IL-6 are not captured.,Selection and referral bias inherent to a single academic center in Italy limits generalizability across ethnically, socioeconomically, and clinically diverse TRD populations.,Potential confounding by concomitant medications (e.g., anti-inflammatory agents, antipsychotics, antidepressants with immunomodulatory properties), comorbid medical illnesses, BMI, and lifestyle factors affecting IL-6 levels—not addressed in the abstract.,Open-label design introduces significant risk of performance and detection bias in subjective rating scale assessments (MADRS).,Conflict of interest: lead author has financial relationships with Janssen-Cilag S.p.A. (esketamine manufacturer), which could introduce reporting or interpretation bias, even if this work is declared independent.,Abstract-only availability (noted per protocol): additional methodological details, full statistical outputs, and sensitivity analyses may exist in the full text but could not be reviewed. __BOTTOM_LINE_CATEGORY__ promising_but_preliminary __BOTTOM_LINE__ In a preliminary open-label trial of only 14 TRD patients, higher baseline serum IL-6 was associated with faster depressive symptom reduction with intranasal esketamine, suggesting a potential role for inflammatory biomarker-guided patient selection. These findings are strictly hypothesis-generating: the sample is far too small, the design uncontrolled, and the statistical outputs incompletely reported to support any modification of current esketamine prescribing practice. Adequately powered, placebo-controlled, biomarker-stratified trials are required before IL-6 can be considered a clinically actionable predictor of esketamine response.