Initial Severity and Diagnosis Influence the Relationship of Tricyclic Plasma Levels to Response

There is considerable controversy about the clinical value of monitoring tricyclic antidepressant plasma levels. To investigate this issue the authors pooled data from 17 published plasma level studies of imipramine, amitriptyline, or nortriptyline, involving over 400 patients. The findings suggest that tricyclic antidepressant plasma level monitoring is important primarily for patients who are severely depressed or who have endogenous features. Monitoring is especially important for such patients who are treated with amitriptyline or nortriptyline, since failure to respond may be associated with very low or very high plasma levels. These data have implications for tricyclic antidepressant plasma level monitoring and future research.