Desipramine plasma levels and clinical response: evidence for a curvilinear relationship.

Twenty-six outpatients with major depression completed a 6-week, fixed dose trial of desipramine and provided plasma samples. Recovery after 6 weeks, defined in either of two ways, corresponded to lower desipramine levels, while clinical status at 4 weeks bore no apparent relationship to plasma levels. Upper limits of 140 or 155 ng/ml emerged depending on the outcome measure used. Patients with endogenous depression, those with primary depression, and those with abnormal dexamethasone suppression test results yielded similar therapeutic thresholds, while the sharpest blood level/response relationship emerged in the subgroup with an abnormal escape from dexamethasone.