Plasma levels of antidepressants after their withdrawal

The period of elimination of tricyclic antidepressant amitriptyline was studied both in plasma and erythrocytes and the influence of the preparation of blood element samples on the elimination of residual antidepressant was examined. Also the effect of stress on antidepressant level was studied. Amitriptyline was not found in plasma 14 days after its withdrawal, while at the same time its levels in erythrocytes were still well measurable. Repeated washing of erythrocyte membranes did not eliminate the residual drug completely. Demethylase activity was found to be enhanced by stress. It is suggested that all results of antidepressant binding studies may be influenced by residual drug concentration in tissues. Interindividual variability may be caused by various intensity of stress mechanisms related to depressive disorders.