Change in Tacrolimus Concentration Measured in Whole Blood Correlates With Changes in Red Blood Cell Parameters After Red Blood Cell Transfusion in Kidney Transplant Recipients.

• Tacrolimus (TAC) concentration was increased by red cell concentrates transfusion. • TAC rate had a significantly strong positive correlation with red blood cell parameter rates. • The changes in whole-blood TAC concentration and red blood cell parameters were correlated • The relationship in kidney transplant recipients was assessed for the first time. Tacrolimus (TAC) is a narrow therapeutic range drug that requires therapeutic drug monitoring. TAC concentration is measured using whole blood owing to its high red blood cell (RBC) transfer rate of 95%. The distribution and whole-blood TAC concentration may be affected by the transfusion of red cell concentrates (RCCs); however, this has not been studied in kidney transplant recipients (KTR). Therefore, we investigated the relationship between changes in whole-blood TAC concentration and RBC parameters before and after RCC transfusion in KTR. Fifteen KTR who received TAC and RCC transfusions were enrolled. The change rates of RBC parameters (RBC count, hemoglobin [Hgb], hematocrit [Hct]), and TAC concentration/dose before and after transfusion were calculated. The correlation between each RBC parameter and the TAC rate was evaluated. The TAC concentration and rate increased after RCC transfusion. Moreover, the TAC rate showed a significant and strong correlation with RBC count, Hgb, and Hct, with RBC count showing the highest correlation coefficient (r = 0.811, 0.766, and 0.764, respectively; p <.01). Serum creatinine and potassium levels remained stable, suggesting the absence of typical adverse effects associated with TAC, such as acute kidney injury or hyperkalemia. Changes in whole-blood TAC concentration and RBC parameters were correlated, and whole-blood TAC concentration increased after RCC transfusion. Therefore, the TAC dose should be adjusted accordingly. [ABSTRACT FROM AUTHOR]