Therapeutic drug monitoring (TDM) in neurology

TDM relies on the quantitative determination of drugs in biological fluids. Since its introduction in the early sixties, TDM has gone through major steps of development, from a drug assay-oriented to a patient-oriented approach. The acronym TDM is retained, but it is intended as "management" instead of "monitoring" to emphasize the actual role of laboratory measurement in therapy handling. In the field of neurology, TDM is a long recognized tool in the clinical management of epilepsies. Moving from our experience in antiepileptic TDM, in this paper we critically revise the pharmacologic and methodologic requirements for a correct application, interpretation and use of TDM in optimizing individual patient drug treatment. The "reference range" concept and its limitations are thoroughly discussed. Experimental evidence is also provided outlining the role of TDM in the post-marketing, real-world characterization of clinical and toxicological profiles of new drugs.