Immunosuppressant drug monitor: A non-invasive device to measure tacrolimus level in the saliva of transplanted patients

Solid organ and vascularized composite allograft transplantation are pivotal in enhancing both life expectancy and quality of life. However, the significant risk of donor tissue rejection requires lifelong immunosuppressive therapy. Tacrolimus, a common component of immunosuppressive regimens, offers effectiveness in preventing organ rejection but poses challenges due to its narrow therapeutic window and toxicity, making it essential to carefully monitor its concentration. Tacrolimus trough levels are currently measured in blood, requiring frequent blood draws from patients, and results are available after 3 to 6 h. To address the need for a fast, minimallyinvasive, and simple method to monitor tacrolimus concentrations, we have assessed a new device for athome analysis, the Immunosuppressant Drug Monitor (IDM) that can extract, identify and quantify tacrolimus in saliva within 15 min. We included males and females hospitalized at Massachusetts General Hospital Transplant Unit, between the ages of 21 and 65 years, and treated with Tacrolimus. Informed consent, demographic and treatment data were collected. Each subject was asked to provide a 5 mL saliva sample that was de-identified and processed by the IDM, while a 5 mL blood sample was drawn and supplied to the MGH clinical lab for analysis by the current standard, immunoassays. The predicted tacrolimus concentration found in saliva was compared to the blood trough level results. 62 samples from 31 different patients were obtained. The male to female ratio and ethnicity distribution were well balanced. The majority of patients were within 30 days of initiating tacrolimus treatment. After IDM calibration and exclusion, 21 samples were measured by the IDM. Using an exponential function fit, the IDM showed a correlation of R2 = 0.39 between the saliva Test Line absorption and the measured tacrolimus concentration in blood, with an average absolute error of 1.8 ng/mL. Our results demonstrate a clear correlation between blood and saliva measurements. The IDM provided promising results to monitor immunosuppressant drug concentrations in patients after transplantation. Future larger studies will further develop the correlation, and the IDM's potential impact on patient outcomes.