Background: Ketamine has emerged as a promising pharmacotherapy for depression and other mental illnesses, and the intramuscular (IM) administration of ketamine is now offered at many North American outpatient psychiatric clinics. However, a characterization of the outpatient population receiving IM ketamine treatment, and an evaluation of the real-world efficacy and safety of long-term IM ketamine treatment, has not been reported.

Objectives: To evaluate the clinical characteristics, treatment patterns, clinical outcomes, and adverse events of patients receiving IM ketamine treatment.

Methods: Patient data from a private outpatient psychiatric clinic’s EHR were collected and analyzed retrospectively. Adults who received ketamine treatment only by IM administration from January 2018 – June 2021 were included.

Results: Patients receiving IM ketamine treatment had a mean of 2.8 (SD 1.4) psychiatric diagnoses, and major depressive disorder was the most common diagnosis (420 (93%) patients). Thirty-seven percent (42/114) of patients reported a history of a previous suicide attempt, and patients had an average of 3.1 (SD 2.9) psychiatric medication prescriptions at baseline. Patients received between 1 and 48 IM ketamine treatments. Average depression and anxiety symptoms significantly improved (p < .001) from baseline (PHQ-9: mean=16.3, SD=6.7; GAD-7: mean=12.8, SD=5.7) to patients’ last treatment (PHQ-9: mean=10.8, SD=5.9; GAD-7: mean=8.4, SD=5.5), and suicidal ideation scores also significantly improved (p < .001). With maintenance ketamine treatments, median improvements in depression and anxiety of at least 21% and 19% were maintained for over 13 months. An adverse event occurred during 59 of 2,532 treatments (2.3%).

Conclusion: IM ketamine is being utilized to treat psychiatric outpatients with a moderate-to-severe mental health history and multiple mental illnesses not limited to depression. IM ketamine treatment shows a strong real-world safety profile, and mental health symptoms significantly improve throughout treatment. Further prospective studies are recommended to confirm the long-term efficacy and safety of IM ketamine.