Tacrolimus whole blood concentrations correlate closely to side-effects in renal transplant recipients

Aims To evaluate the relationship between tacrolimus whole blood concentrations and side-effects and rejections in 14 renal transplant recipients. Methods Tacrolimus was measured by MEIA in whole blood in samples collected repeatedly during the first year after transplantation. Retrospectively, tacrolimus trough concentrations on the days with adverse events (n = 172) or rejection (n = 28) were related to the total distribution of the concentration values (n = 656). Results Side-effects (one or more) were noted in connection with 76% of tacrolimus concentrations above 30 ng ml(-1), with 41% of concentrations within the interval of 20-30 ng ml(-1), with 26% of the concentrations within the interval of 10-20 ng ml(-1) and with only 5.3% on the concentrations lower than 10 ng ml(-1). No relation to the tacrolimus concentration was seen for rejection episodes. Conclusions We conclude that therapeutic drug monitoring may be helpful in the management of tacrolimus therapy and that tacrolimus whole blood trough concentrations (MEIA) should preferably be kept below 20 ng ml(-1) to avoid side-effects, such as nephro-and neurotoxicity and infections. The lower limit of the therapeutic range has yet to be defined.