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

Aims To evaluate the relationship between tacrolimus whole blood concentrat ions 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, t acrolimus trough concentrations on the days with adverse events (n = 172) o r rejection (n = 28) were related to the total distribution of the concentr ation values (n = 656). Results Side-effects (one or more) were noted in connection with 76% of tac rolimus concentrations above 30 ng ml(-1), with 41% of concentrations withi n the interval of 20-30 ng ml(-1), with 26% of the concentrations within th e interval of 10-20 ng ml(-1) and with only 5.3% on the concentrations lowe r than 10 ng ml(-1). No relation to the tacrolimus concentration was seen f or 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 avoi d side-effects, such as nephro-and neurotoxicity and infections. The lower limit of the therapeutic range has yet to be defined.