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Previous studies have demonstrated ketamine to have a rapid antidepressant effect in some patients with treatment-resistant depression (TRD), but the effect is unfortunately not sustained in the long term. In this study, we report on the clinical use of ongoing maintenance ketamine infusions in a group of patients with TRD, beyond an acute course of 6 to 8 ketamine infusions.This retrospective case series reports on 11 patients with TRD who received maintenance ketamine infusions, defined as treatments beyond an initial series of up to 8 infusions. Charts were reviewed to collect data on response to treatment and side effects.All 11 patients in this case series were noted to have a reduction in their Beck Depression Inventory II (BDI-II) score after an acute course of treatment and a lower median BDI-II during their maintenance treatments than their baseline BDI-II. At the study end point, 4 patients were continuing maintenance ketamine and 1 patient had transitioned to maintenance intranasal ketamine. Four patients discontinued ketamine due to loss of effect and 1 due to side effects, and the reason for discontinuation was not noted for the remaining 2 patients. No major adverse events were noted in these patients receiving maintenance treatments, and it was well tolerated overall.Maintenance ketamine treatments may be an effective way of maintaining treatment response in some ketamine responders. Future research is required to determine optimal length of treatment in those who respond to ketamine and to track adverse effects over a longer time.