Desipramine plasma concentration and antidepressant response.

The relationship of desipramine hydrochloride plasma concentration and antidepressant response was determined in 30 depressed inpatients treated for three weeks with desipramine. All patients had a nondelusional unipolar depression, met DSM-III criteria for major depressive episode with melancholia, and had a Hamilton score of 18 or greater after one week of hospitalization without medication. Eighty-nine percent of the patients with plasma concentrations above 115 ng/mL responded, in contrast to 14% of those with concentrations below this level, a significant difference (Fisher's exact test, P less than .001). Ten initial nonresponders were converted to responders when dosage increase raised desipramine plasma concentration to 125 ng/mL or above. In clinical practice a plasma concentration of 125 ng/mL would be a useful guideline as a threshold above which desipramine is likely to be effective.