Recent advances in therapeutic drug monitoring of immunosuppressive drugs

• The therapeutic drug monitoring of immunosuppressants is ambitious due to many factors.
• The gold standard LC-MS/MS has been adapted and applied to alternative matrices.
• Immunoassays enable measurements in shorter time intervals compared to LC-MS/MS.
• The interpretation of analytical values, obtained by various techniques remains crucial.

The transplantation of a solid organ is always followed by a lifelong immunosuppressive therapy to guarantee the survival of the organ in the recipient. Immunosuppressive drugs have to be applied in order to preserve the graft and at last the patient's life. These drugs are strongly recommended for therapeutic drug monitoring (TDM) in order to adjust the adequate dose for each patient to avoid rejection or adverse effects of the therapy. This finely tuned therapy would not be possible without the proper analytical tools and techniques. Either chromatography methods or immunoassays based on e.g. fluorescence or colorimetric detection principles are used in practice.All of them have to cope with the challenging, individually differing matrix whole blood. It is difficult to reach the relevant levels of quantification.The focus of this review is on the explanation, comparison and future outlook of the current analytical techniques for TDM of immunosuppressants.