Replication of distinct trajectories of antidepressant response to intravenous ketamine.

BACKGROUND: The goal of this study was to replicate previous findings of three distinct treatment response pathways associated with repeated intravenous (IV) ketamine infusions among patients with major depressive disorder (MDD). METHODS: We conducted growth mixture modeling to estimate latent classes of change in depression (Quick Inventory of Depressive Symptomatology-Self Report, QIDS-SR) across six treatment visits in 298 patients with MDD treated with IV ketamine in an outpatient community clinic. Mean age was 40.36 and patients were primarily male (58.4 %). The sample had relatively severe depression (QIDS-SR = 16.61) at pre-treatment and the majority had not responded to at least two prior medications. RESULTS: Best-fit indices indicated three trajectory groups to optimally demonstrate non-linear, quadratic changes in depressive symptoms during ketamine treatment. Two groups had severe depression at baseline but diverged into a group of modest improvement over the treatment course (n = 78) and a group of patients with rapid improvement (n = 103). A third group had moderate depression at baseline with moderate improvement during the treatment course (n = 117). Additional planned trajectory comparisons showed that suicidality at entry was higher in the high depression groups and that change in suicidality severity followed that of depression. LIMITATIONS: This was a retrospective analysis of a naturalistic sample. Patients were unblinded and more heterogenous than those included in most controlled clinical trial samples. CONCLUSIONS: This replication study in an independent community-based ketamine clinic sample revealed similar response trajectories, with only about a third of depressed patients benefitting substantially from an acute induction course of ketamine infusions.