ABSTRACT
Organ transplantation in the final stages of chronic disease or in case of acute failure is an accepted procedure of treating patients that has been developing for many years. After the organ transplantation procedure, immunosuppressive therapy is started, which strikes a balance between the modulation of the immune system in order to avoid organ rejection or the harmful effects of immunosuppression. Commonly used immunosuppressants for the treatment of transplant patients are from the group of calcineurin inhibitors (cyclosporine, tacrolimus) and mTOR inhibitors (sirolimus, everolimus). Mycophenolic acid, leflunomide and glucocorticoids are used as supportive therapy, and with the discovery of biological therapy, therapeutic monoclonal antibodies directed against various cellular targets have been developed. Optimization and laboratory monitoring of immunosuppressive concentrations is necessary after transplantation in order to avoid graft rejection and the occurrence of unwanted side effects. The most commonly used methods for therapeutic drug monitoring in clinical laboratories are immunochemical methods characterized by high levels of automation but also have major shortcomings such as insufficient specificity and standardization, which is why the method of choice for therapeutic monitoring is liquid chromatography-tandem mass spectrometry whose main characteristic is specificity and selectivity. Therefore, when measuring the concentration of immunosuppressants, it is important to state the method of determination. The global spread of Coronavirus disease (COVID-19) has affected organ donation and transplantation and is actively trying to clarify the role of immunosuppressive therapy in the disease process because it is extremely difficult to strike a balance between suppressing the immune response to prevent organ rejection and control inflammation during COVID-19 disease. Given the complexity of treating the transplant population of patients with COVID-19, there is a clear need for a systemic approach to treatment, which will consequently lead to better outcomes.