Therapeutic drug monitoring of antidepressants - Cost implications and relevance to clinical practice

Despite evidence to support its potential benefit in clinical practice, the rapeutic drug monitoring (TDM) is under-utilised and underdeveloped in the field of psychiatry. In antidepressant pharmacotherapy drug dose is emphasi sed as the critical treatment variable. However, dose in, and of, itself ca n be a strikingly misleading predictor of drug concentration and, hence, tr eatment effect. For antidepressant drugs, plasma concentrations at a given dose have been shown to vary in excess of 40-fold. The clinical relevance o f this variability is that at a standard antidepressant dosage only some pa tients will have tissue drug concentrations associated with an optimal resp onse whereas others will have either low, ineffective drug concentrations o r unnecessarily high concentrations which may be poorly tolerated. Among clinicians and healthcare agencies there is an under-appreciation of the degree of pharmacokinetic variability found in patients and how that mi ght impact on the patients response to pharmacotherapy. Hence there is a pe rception that TDM is an unnecessary, complicated and costly procedure. This is actually unfounded. There are data to suggest that TDM can favourably a ffect the outcome of antidepressant treatment by providing a rational alter native to the inherently slower, trial and error practice of dosage titrati on based on clinical response. It is unlikely that TDM will become a standard of care for all antidepressa nt agents and all patients. Therefore the question becomes for which antide pressant agents, for which patients and under what circumstances, is TDM mo re cost-effective than traditional dose titration. The use of TDM to optimi se the efficient use of selected antidepressant agents could potentially fr ee up healthcare resources to fund other equally deserving treatments. This article provides a discussion of the major classes of antidepressant drugs with regard to their pharmacological features that predict the utility of TDM in clinical practice. Recommendations are made for the practical applic ation of TDM and the directions for further research.