Background: A rapid antidepressant effect of ketamine has repeatedly been documented in the literature, and identifying clinical features associated with a better response to this treatment is currently an essential question. Considering the relationship between rumination and depression and the need to identify potential predictors of response to ketamine, we analyzed the effect of a single injection of ketamine 0.5 mg/kg on rumination in treatment-resistant depressive (TRD) patients and explored whether baseline ruminative style and early improvements of rumination would predict a greater antidepressant effect of ketamine.
Methods: Ten TRD outpatients who participated in a 4-week open study on the antidepressant effect of ketamine also completed the Ruminative Response Scale the day before, the day after, and a week after ketamine administration.
Results: We found that in our patients, a single rapid 1-minute intravenous injection of ketamine 0.5 mg/kg was efficacious in reducing rumination, but neither severity of rumination at baseline nor early improvements of rumination after ketamine injection predicted antidepressant response.
Conclusions: Our preliminary data suggest that a single injection of ketamine 0.5 mg/kg can be efficacious in reducing rumination in TRD patients but rumination does not seem to be a useful clinical predictor of response to ketamine. Larger studies are necessary to confirm these results.