We investigated the serial changes in the blood CsA concentration during the switch from continuous intravenous infusion to twice-daily oral administration in allogeneic hematopoietic stem cell transplant recipients (n=12). The microemulsion form of CsA, Neoral, was started at twice the last dose in intravenous infusion in two equally divided doses. The area under the concentration-time curve during oral administration (AUC PO) was significantly higher than the AUC during intravenous infusion (AUC IV) (median 7508 vs 6705 ng/ml × h, P=0.050). The median bioavailability of Neoral, defined as (AUC PO /DOSE PO) divided by (AUC IV /DOSE IV), was 0.685 (range, 0.45-1.04). Concomitant administration of oral voriconazole (n=4) significantly increased the bioavailability of Neoral (median 0.87 vs 0.54, P=0.017), probably due to the inhibition of gut CYP3A4 by voriconazole. Although the conversion from intravenous to oral administration of CsA at a ratio of 1:2 seemed to be appropriate in most patients, a lower conversion ratio may be better in patients taking oral voriconazole. To obtain a similar AUC, the target trough concentrations during twice-daily oral administration should be halved compared with the target concentration during continuous infusion.
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