Therapeutic Drug Monitoring of Antidepressants

Abstract

Therapeutic drug monitoring (TDM) can play an important role in use of a number of antidepressants and other psychotropic medications (e.g., tricyclic antidepressants). However, the field of psychiatry has been slow to adopt such monitoring as a routine part of care. Research supporting the clinical benefit and cost-effectiveness of TDM with newer antidepressants has also been limited. However, an increasing awareness of how significant inter- and intra-patient variability in pharmacokinetics may affect response to antidepressant therapy is creating growing interest in the use of TDM to optimize antidepressant treatment response. To interpret the results of TDM, it is important to understand the relationship between plasma and tissue concentrations of drugs and the factors that can cause variations in drug concentration. There is a correlation between plasma concentrations of psychotropic drugs and tissue concentrations. Thus, TDM provides an indirect measurement of drug concentration at effector sites in tissue compartments of interest (i.e., the central nervous system for psychotropic medications). Plasma drug concentrations of a given dose of drug may be affected by the pharmacokinetics of the individual patient (e.g., drug absorption, metabolism, elimination). TDM can be used to increase the safety of antidepressant pharmacotherapy with certain agents (e.g., tricyclic antidepressants) by enabling clinicians to avoid toxic levels of medication resulting from variations in patient pharmacokinetics. TDM can also be used to enhance therapeutic response. For those antidepressants with established concentration:response relationships, TDM has the potential to speed antidepressant response by providing a basis for more efficient dose adjustment and can also help clinicians monitor/confirm medication compliance. Recommendations for the use of TDM in clinical practice and directions for future research are provided.