Mark J Niciu, Beth DG Grunschel, Philip R Corlett, Christopher Pittenger, Michael H Bloch

Ketamine is a non-competitive N-methyl-D-aspartate receptor antagonist that is Food and Drug Administration-approved in the United States for anesthesia due to its sedative effects with low risk of severe respiratory depression. Subanesthetic dose intravenous ketamine has rapidly acting antidepressant effects in treatment-resistant unipolar and bipolar depression. We recently reported an open-label trial of ketamine in 10 subjects with treatment-refractory obsessive-compulsive disorder, seven of whom had active comorbid depression. Although ketamine had no sustained anti-obsessive effect, four of the seven subjects with comorbid depression experienced an acute antidepressant effect. However, we unexpectedly observed delayed-onset dysphoria, worsening anxiety and suicidal thinking in two of the three subjects with obsessive-compulsive disorder and extensive psychiatric comorbidity but minimal depressive symptoms at the start of infusion. The implications of these adverse neuropsychiatric effects in two patients with similar psychiatric comorbidity are discussed. We conclude that there remains insufficient data on therapeutic ketamine in the presence of comorbid psychiatric disorders to promote its off-label use in a non-research milieu.