Madsen T, et al. - Given that patients with major depressive disorder (MDD) frequently experience suicidal ideation, researchers investigated the differential development during antidepressant treatment and if suicidal ideation persists in some patients. Among 811 patients with Schedules for Clinical Assessment in Neuropsychiatry (SCAN)–verified MDD from 2004–2007 who had weekly evaluations for 12 weeks of escitalopram or nortriptyline antidepressant treatment, five distinct classes of suicidal ideation were identified: persistent-low class (53.7%) presented no suicidal ideation; persistent-high class (9.8%) presented high suicidal ideation; fluctuating class (5.2%) finished at a low level of suicidal ideation; slow-response-relapse class (4.8%) showed slow response initially but then had a large increase to a high level of suicidal ideation after 12 weeks; and fast-response class (26.5%) exhibited a high baseline severity comparable to persistent-high class but responded promptly within a few weeks and continued at a low level. These findings suggest the presence of high or fluctuating suicidal ideation in approximately 1 of 5 patients with MDD despite antidepressant treatment.