Real world effectiveness of maintenance ketamine infusions for treatment-resistant depression in major depressive disorder and bipolar disorder.

Antidepressant effects with sub-anesthetic doses of intravenous ketamine have been previously demonstrated. However, previous studies have primarily evaluated the efficacy of acute treatment protocols, with limited research on maintenance treatment. Moreover, controlled maintenance studies have only included patients with treatment-resistant Major Depressive Disorder (TRD), with no maintenance studies evaluating effects in bipolar disorder. Herein, we report the first study to evaluate maintenance ketamine infusions in patients with treatment-resistant bipolar depression (TRBD), in addition to a sample of patients with TRD. A retrospective chart review of patients receiving ketamine infusions from a community treatment centre was conducted. 110 TRD and 25 TRBD patients were included, all of whom responded to an acute course of ketamine infusions and later received maintenance infusions. Linear mixed models found that depression and suicidality scores, as measured by the Quick Inventory of Depressive Symptomatology (QIDS-SR16) assessment, were significantly decreased after an acute course of ketamine infusions, with improvements persisting while patients continued to receive maintenance infusions over several weeks and months. Similar observations were seen after analyzing weekly patient-reported clinical global impression scores. Ketamine was determined to be relatively safe, with zero cases of suicidal behaviour and addiction behaviour throughout treatment. One patient (4 %) diagnosed with TRBD underwent affective switching, with no further tolerability concerns following stabilization. These results provide preliminary support for the long-term clinical utility of maintenance ketamine infusions.