Since TDM assay results have a great impact on medication treatment, accuracy of TDM report is vital. On the other hand, it should be considered that some factors may have change blood medication levels. These are age, gender, body weight, diseases, pregnancy, lactation medication interactions, pharmacogenetics and blood sampling time.

Various analytical methods have been used for TDM service and investigations. These are mainly chromatographic (GC-MS, HPLC, LC-MS) and immuno binding assays methods (Fluorescence Polarization Immuno Assay-FPIA, Enzyme Immunoassay-EMIT, enzyme-linked Immunosorbent assay and Chemiliumericense). Although immunoassays are more economic and fast than chromatographic methods, their sensitivity, specificity, and accuracy concerning the target medication is lower than chromatographic techniques.

Enormous technical developments in molecular biology methods and understanding of our genome function have been given prominent contribution to medication treatment especially in last two decades. Number of actionable pharmacogenetics biomarkers has been increasing for considerable number of medications [2]. Thus, combination of genotyping for particular medications together with TDM has a great potential to achieve successful treatment with minimising adverse drug reactions in pharmacotherapy. Keywords : Therapeutic Drug Monitoring (TDM); genotyping; pharmacotherapy