PHARMACOKINETICS OF TACROLIMUS (FK506) IN PEDIATRIC LIVER-TRANSPLANT RECIPIENTS

The pharmacokinetics of intravenous and oral tacrolimus was assessed i n paediatric liver transplant patients at two centers in Europe. Sixte en patients, age 0.7 to 13 years, participated in the study; 12 patien ts were evaluable for intravenous pharmacokinetics, and 16 for oral. I ntravenous tacrolimus was given as a continuous 24 h infusion (mean 0. 037 +/- 0.013 mg/kg/day), and oral tacrolimus was given in 2 doses per day (mean 0.152 +/- 0.015 mg/kg). Whole blood samples for the intrave nous pharmacokinetic profile were taken before initiation of the first infusion, 4, 8, 12 and 24 h post-infusion, and every 24 h thereafter until intravenous administration was discontinued. During the 12 h was h-out period between intravenous and oral administration, samples were taken every 3 h. Samples for the oral pharmacokinetic profile were ta ken immediately before the first oral dose and 0.5, 0.75, 1, 2, 2.5, 3 , 4, 6, 8, 10 and 12 h post-administration. Non-compartmental procedur es were used to characterise the pharmacokinetic parameters. Mean esti mates for clearance and terminal half-life were 2.3 +/- 1.2 ml/min/kg and 11.5 +/- 3.8 h, respectively, following intravenous tacrolimus. Th e mean bioavailability of oral tacrolimus was 25 +/- 20%. A strong cor relation was observed between AUC and trough whole blood levels of tac rolimus (r = 0.90). The clearance was approximately 2-fold higher than that previously observed in adults; this could explain the higher dos age requirements in children.