High plasma nortriptyline levels in the treatment of depression. I

Following a 3-day single-dose kinetic study, 21 moderate to severely depressed inpatients were treated with 100 mg of nortriptyline nightly. Eighteen patients completed the 4-wk trial. The severity of depression was measured by weekly Hamilton Rating Scale and global rating. Blood for plasma nortriptyline estimation was taken at weekly intervals 12 h following the nighttime dose. There was a 6-fold variation in mean plasma nortriptyline levels, ranging from 120 microgram/L to 681 microgram/L. Patients with high plasma levels (greater than 200 microgram/L) showed significantly poorer clinical responses than those with levels in routine treatment, high plasma nortriptyline levels are significantly less effective than intermediate levels. Single-dose pharmacokinetic data obtained on the same patients showed a highly significant correlation with mean steady-state plasma levels obtained, which themselves correlated with clinical response. The value of predicting high plasma nortriptyline levels which are associated with poor response is discussed.