Endogenous depression and imipramine levels in the blood.

Approximate determinations of imipramine plus desmethylimipramine levels in the blood made by a method available in routine clinical chemistry laboratories, in 20 nondelusional endogenous depressives after 3 weeks of treatment (mean dose 130 mg/day, SEM 18.05 mg/day) have shown levels ranging from 10 ng/ml to 494 ng/ml. A positive significant correlation between blood levels and percentage change in scores on the Hamilton scale was found (Spearman's O = 0.49 P < 0.05). Patients with levels above 85 ng/ml had a significantly better therapeutic response than patients with levels below 85 ng/ml. Among the 11 nonresponders, 8 had low levels, 2 had intermediate levels, and 1 had the highest level of the study. In a given nonresponder, approximate determination of imipramine plus desmethylimipramine in the blood may be useful.