Therapeutic Drug Monitoring - A Posteriori Therapeutic Drug Monitoring

• includes pre-analytical, analytical and post-analytical phases, each with the same importance;
• is most often based on the specific, accurate, precise and timely determinations of the active and.or toxic forms of drugs in biological samples collected at the appropriate times in the correct containers (PK monitoring), or can employ the measurement of a biological perimeter as a surrogate or end-point marker of effect (PD monitoring) e.g. concentration of an endrogenous compound, enzymatic activity, gene expression, etc. either as a complement to PK monitoring or as the main TDM tool;
• requires interpretation of the results, taking into account pre-analytical conditions, clinical information and the clinical efficiency of the current dosage regimen; this can be achieved by the application of PK-PD modeling;
• can potentially benefit from population PK/PD models possibly combined with individual pharmacokinetic forecasting techniques, or pharmacogenetic data.

—IATDMCT Executive Committee, Definition of TDM