[Treatment resistant depression: Challenges and therapeutic choices].

Treatment resistant depression is associated with serious and persistent symptomatology, chronic course, reduced quality of life, high rates of comorbidity with medical conditions or other mental disorders, increased indirect health care cost, increased suicidality and risk for hospitalization, negative impact to patients' functioning and occupation and poor treatment outcomes in general. The concept of treatment resistant depression emerged in the 1970s to describe a group of patients suffering from major depressive disorder who failed to reach remission of symptoms after at least two trials with antidepressant (efficient regarding dosage, compliance, and duration). Despite the introduction of many antidepressants over the following years, a large proportion of depressed patients fail to respond to available treatments, and this constitutes a continuing therapeutic challenge.