Monitoring and interpretation of antidepressant plasma concentrations

A brief review of the factors influencing plasma tricyclic concentrations and the relationship between clinical response and plasma concentration is presented. It is concluded that routine monitoring of tricyclics is unwarranted. In some specific instances monitoring tricyclic antidepressant plasma concentrations may be indicated: in cases of therapeutic failure a low level may indicate poor compliance or rapid metabolism and the need to increase the dose; for the management of side effects, especially when cardiac abnormalities exist prior to therapy; in cases of polypharmacy when drug interactions can occur; the management of overdoses and in patients with physical illnesses especially renal and hepatic disease. The elderly also constitute a group of patients in whom drug monitoring may be advisable. This group of patients tends to develop higher plasma levels than younger patients on equivalent doses. Some guidelines for the interpretation of laboratory results are presented and discussed.