Protriptyline plasma levels and antidepressant response.

Twenty-one depressed outpatients were treated for 4 wk with 20 mg/day of protriptyline. Protriptyline plasma in individuals after 4 wk ranged from 22 ng/ml to 167 ng/ml. There was a negative correlation (-0.50, less than 0.05) between the severity of depression measured by the Hamilton Rating Scale (HRS) and the wk 4 protriptyline concentration. Patients with plasma levels above 70 ng/ml (wk 4) had better outcomes measured by the HRS (p less than 0.05) and the Zung Self-Rating Depression Scale (p less than 0.05) and had greater percent decreases on both scales (p less than 0.05) during treatment than those with lower plasma levels. An upper limit to the therapeutic plasma level range beyond which response to treatment was less satisfactory was not demonstrated in this study.