Intranasal Ketamine for Late-Life Depression and Suicidal Ideation

Inclusion Criteria: 1\) be ≥65 years old, 2) provide written informed consent, 3) meet criteria for a primary psychiatric diagnosis of major depressive disorder according to the Structured Clinical Interview for DSM-IV (SCID) and have a HDRS28 total score ≥20; depression may have started at any time point in their life, and certain co-morbid diagnoses (e.g., anxiety disorders) will be allowed insofar as they are not the primary psychiatric diagnosis, 4) have a history of ≥2 failed medication trials during the current episode (per the Massachusetts General Hospital Antidepressant Treatment History Questionnaire; MGH ATRQ), 5) endorse suicidal ideation for more than 2 months, per the Columbia Suicide Severity Rating Scale (C-SSRS) and have a HDRS28 suicide item score ≥1 (thoughts that life isn't worth living), 6) be on a stable antidepressant regimen for ≥14 days prior to Study Phase II, 7) maintain a treating psychiatrist who is in agreement with study participation, and 8) have a reliable chaperone accompany them home following the completion of the intranasal administration. Exclusion Criteria: * Patients will be excluded if any of the following criteria are met: 1) Delirium or dementia diagnosis, 2) unstable medical illness, 3) history of clinically significant cardiovascular disease or electrocardiogram (EKG) findings, or medical conditions that put the patient at risk for possible cardiac side effects, 4) history of multiple adverse drug reactions, 5) current/past history of psychotic disorders or homicidality, 6) active substance use disorders (except nicotine and caffeine) within the past six months, positive urine toxicology screen, or past history of ketamine abuse, 7) requirement of excluded medications (narcotics, barbiturates, theophylline, or St. John's Wort), or 8) concurrent or recent participation in other research studies.