Therapeutic Drug Monitoring of Immunosuppressants in Cardiac Transplantation: Current Strategies, Evidence Gaps, and Future Directions.

Therapeutic drug monitoring (TDM) remains central to managing immunosuppression in cardiac transplantation, especially during the dynamic early post-transplant period, when shifting hematocrit, gastrointestinal absorption, and hemodynamics drive pronounced variability. This review outlines the current TDM practices and highlights how sample collection accuracy, assay-specific analytical considerations, and clinical context shape the interpretation of immunosuppressant levels. Key physiologic, genetic, and methodological factors contributing to variability are summarized, along with the practical barriers to standardization across centers. Emerging technology and methodologies are also reviewed, highlighting opportunities to enhance personalized immunosuppression and facilitate a more consistent assessment of drug levels in cardiac transplant recipients.