Pharmacokinetics and Bioavailability of Oral Ifosfamide

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Abstract
SummaryThe bioavailability of oral N,3-bis(2-chloroethyl)tetra-hydro-2H-l,3,2-oxazaphos-phorine-2-amine-2-oxide (ifosfamide; 500 mg gelatine capsules) was investigated in 18 patients with bronchogenic carcinoma. Oral and intravenous (Holoxan®) ifosfamide was administered in a randomized sequence on days 1 and 3 at a dose of 1 g/m2 B. S. A. (n = 12) and 2 g/m2 B. S. A. (n = 6). Ifosfamide determination was performed with N/P flame ionization gas chromatography following derivatization with heptafluorobutyric acid. Orally administered ifosfamide showed relatively fast absorption kinetics. Peak levels were reached within 1 h in both dosage groups. With the exception of the absorption phase, blood level curves of orally and i. v. administered ifosfamide were identical. The average half-life of ifosfamide was 5.5 h (2 g/m2 B. S. A.) and 5.8 h (1 g/m2 B. S. A.) with a considerable individual variation in both dosage groups.The bioavailability of oral ifosfamide calculated as ratio AUCp.o/AUCi.v. was 1.04 after 1 g/m2 B. S. A. ifosfamide and 0.95 in the 6 patients receiving 2 g/m2 B. S. A. ifosfamide. According to our results, i. v. administration of ifosfamide, especially in fractionated dosage regimens, can be replaced by oral application of the same ifosfamide dose.

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