Oral vs intravenous tacrolimus-based induction therapy in renal transplantation.

The target blood concentrations of tacrolimus (TAC) and cyclosporine (CYA) during continuous intravenous infusion (Css) have been determined based on clinical experience. However, it is desirable that Css should be set so that the AUC after intravenous infusion is equal to the AUC after oral administration (AUCpo). Accordingly, we performed 12-hour monitoring of blood concentrations to calculate Css from the blood trough levels (CTL) on 15 kidney recipients administered TAC and 12 recipients administered CYA (Neoral). We used an area under the trough level (AUTL) as a new pharmacokinetic parameter. The Css was evaluated from CTL, AUCpo, and AUTL was calculated to be Css = CTL × (AUCpo/AUTL). In addition, AUTL/AUCpo ratio and blood peak/trough level ratio (Cmax/Cmin) were examined to compare pharmacokinetics of TAC and CYA. The formula for TAC was Css = CTL × 1.40 and that for CYA, Css = CTL × 2.55. The calculated target Css of TAC was 1.40 times that of CTL, which was similar to the present clinical CTL. In contrast, the calculated target Css of CYA was 2.55 times the CTL, and therefore an extremely high Css was necessary to obtain a sufficient AUC that will be available after oral administration. Consequently, intravenous administration of CYA twice a day was considered to be more appropriate to obtain sufficient CYA pharmacokinetics, rather than a continuous intravenous administration. We conclude that the formula, Css = CTL × (AUCpo/AUTL) was useful to calculate the target blood concentration of calcineurin inhibitors when changing from continuous intravenous infusion to oral administration of these drugs.