Is there a therapeutic range for monitoring plasma cyclosporin in renal allograft recipients?

Sixty-two consecutive adult cadaveric renal allograft recipients have been monitored by high-performance liquid chromatography estimations of trough plasma cyclosporin (CsA) concentrations within 30 days of transplantation. The CsA estimations during graft rejection (mean + 1 SD 218.6 + 126.4 ng/ml) were not significantly different from those obtained during stable renal function (232.3 + 172.8 ng/ml), whereas the estimations during episodes of nephrotoxicity (476.0 + 267.3 ng/ml) were significantly greater (P less than 0.001). During stable renal function 73.7% of estimations were within the therapeutic range of 100-350 ng/ml. However, 37.9% of estimations during nephrotoxicity and 76.7% of estimations during rejection episodes were also within this range. The therapeutic window for trough plasma CsA estimations is not clearly defined. It seems that rejection episodes may occur at apparently adequate CsA concentrations, and although most nephrotoxic episodes are associated with elevated concentrations, acute nephrotoxicity may occur at apparently therapeutic values. However, in this study, some patients at risk of nephrotoxicity within 30 days of transplantation were identified as early as 7 days post-transplantation by the simple determination of the mean trough CsA concentration for days 1-7.