Higher baseline absolute monocyte count (AMC) predicts greater symptom improvement during intravenous ketamine therapy for treatment-resistant depression. In 27 participants receiving six ketamine infusions over three weeks, baseline AMC showed a strong negative correlation with depression severity change after the first infusion and before the last infusion, meaning higher monocyte levels were associated with more symptom reduction. Baseline AMC distinguished responders and partial responders from non-responders but not between partial and full responders. Absolute neutrophil count correlated weakly with early improvement, while C-reactive protein showed no correlation. AMC may serve as a simple clinical marker for predicting ketamine treatment response.
In adults with treatment-resistant depression receiving six intravenous ketamine infusions over three weeks, higher baseline levels of the neuroprotective metabolite kynurenic acid (KYNA) in the kynurenine pathway were associated with greater symptom improvement by day 18. KYNA remained stable over time and did not track with symptom changes, suggesting it acts as a trait-like marker rather than a state-dependent one. Early shifts toward the neurotoxic branch of the pathway (kynurenine and 3-hydroxykynurenine) were linked to reductions in hopelessness and suicidality scores after the first infusion. These exploratory findings indicate that a kynurenine pathway profile biased toward neuroprotective metabolites may inform future biomarker studies of ketamine response, but require validation in larger samples.
A 42-year-old patient with severe treatment-resistant depression and psychiatric comorbidities attempted suicide five weeks after hospital admission. After starting dextromethorphan/bupropion, her mood improved and suicide risk decreased, allowing discharge.