Tricyclic antidepressants: the whys and hows of therapeutic drug monitoring.

Therapeutic drug monitoring (TDM) of tricyclic antidepressants (TCAs) is a cost-effective tool that can improve both the safety and efficacy of TCA pharmacotherapy. By understanding the principles behind TDM, the physician can rationally interpret plasma TCA levels and avoid spurious results. The following features of TDM of TCAs are reviewed: (1) the relationships between TCA concentration in plasma and the multiple pharmacologic actions and clinical effects of TCAs, (2) the use of TDM to improve antidepressant efficacy while avoiding both cardiac and brain toxicity, (3) the protocol to follow when using TDM of TCAs and the rationale behind it, and (4) common laboratory errors that can be readily avoided but that could otherwise lead to spurious results.