Plasma drug levels and clinical response to antidepressants

Antidepressants are a key treatment in depression. The wide interindividual differences in plasma levels of these agents were initially seen as an explanation for nonresponse and a potential major advance in treating depressive disorders. However, efforts to relate plasma levels to therapeutic outcome have, in general, been disappointing. In the few instances where such relationships have been claimed, they have been weak and useful only for specific and problematic clinical conditions.