Background  As an immunosuppressant, tacrolimus (also known as FK506, TAC) is often used to prevent rejection in renal transplantation or other transplantation. Due to the drug metabolism difference of FK506, the drug concentration needs to be monitored regularly in clinic. However, the change of body state is less reported after the patient maintains a stable drug concentration.

  Objective  To investigate the effects of FK506 concentration on liver and kidney function in renal transplant patients.

  Methods  Clinical data about 192 renal transplant patients with stable FK506 concentration within one year postoperatively were analyzed retrospectively in the First Medical Center of Chinese PLA General Hospital from October to December in 2019. The patients were divided into four groups according to the blood concentration of FK506 by quartile (Q1-Q4). The age, liver function, renal function and whole blood cells were evaluated.

  Results  The median (IQR) drug concentration in the quartile group from low to high was 4.00 (2.95, 4.45) ng/L (n=52, including 14 women), 5.20 (5.00, 5.30) ng/L (n=49, including 17 women), 6.20 (5.85, 6.40) ng/L (n=46, including 19 women), 7.90 (7.50,9.00) ng/L (n=45, including 15 women) (P=0.517). The median (IQR) age of patients in the four groups was 49.0 (42.0, 57.0) years, 45.0 (36.0, 56.0) years, 45.5 (37.0, 53.0) years and 40.0 (32.0, 47.0) years (P＜0.05). eGFR, urea and creatinine showed significant differences among the four groups (all P＜0.05). In male group, with the increase of FK506 concentration, urea and creatinine decreased; eGFR and RBC increased (all P＜0.05); In female group, there was no significant difference in these indexes (P>0.05). There was positive correlations between FK506 level and renal function indexes (urea, creatinine, eGFR) levels (all P＜0.05) in male group. In female group, the correlations between FK506 and all these indexes were not statistically significant (P>0.05).

  Conclusion  On monitoring of renal function after renal transplantation, male patients is prone to be affected to the changes of FK506 concentration, which indicates that protective effect from tacrolimus on renal function may differ by gender and more attention should be paid to gender differences during drug administration and monitoring.