In March of 2019, the US FDA approved intranasal esketamine for treatment-resistant depression (TRD). Conceptually, this is an extraordinary event from the point of view of drug development in psychiatry insofar as this is the first time the FDA has approved an antidepressant medicine that was developed on the basis of an a priori diseases model (i.e. glutamatergic dysregulation relevant to the pathogenesis of mood disorders).
The heterogeneity of treatment response in MDD has provided a compelling rationale for identifying predictors of response/tolerability (and non-response/intolerability) amongst individuals assigned to a given treatment. The need to identify predictors of response is even greater when the treatment options being considered are more costly, require more resources for administration (e.g. specialized clinics), and/or may be associated with greater safety/tolerability concerns.