The use of plasma levels for FK 506 dosing in liver-grafted patients.

FK 506 plasma levels were analyzed in 89 liver-grafted patients under FK 506-based immunosuppression. Plasma levels were found to be influenced by the patients' liver function: compared to patients without major liver dysfunction, those with cholestasis had higher plasma levels and these plasma levels were able to differentiate between rejection and toxicity. In patients with stable liver function, no clear difference was observed with regard to the plasma levels detectable during toxicity or rejection. We conclude that plasma levels can be used to determine the FK 506 dose but only in patients with cholestasis (i.e., during the early post-transplant course, or in patients with cholestatic rejection). In patients with stable liver function, plasma levels are only of limited clinical relevance.