Quantification of 4-hydroxyifosfamide in plasma of ifosfamide-treated mice.

Abstract

Ifosfamide is becoming an important clinical anticancer drug. Meaningful pharmacology studies require quantification of its activated and active metabolites, 4-hydroxyifosfamide (HOIfos) and isophosphoramide mustard (IPM), respectively. Current methodology for quantifying the unstable HOIfos in biological fluids consists of trapping acrolein as it is produced during the decomposition of this metabolite. However, unlike cyclophosphamide, ifosfamide is extensively metabolized to two dechloroethylated metabolites, which are susceptible to 4-hydroxylation and similarly are capable of yielding acrolein upon decomposition. Because the current method has the potential to yield higher than actual values for HOIfos, it was compared with an HOIfos-specific method that traps the first stage degradation product of HOIfos, aldoifosfamide, as its semicarbazone, and depends on the use of radiolabeled drug for quantification. Six experiments in mice were conducted with blood collection 15 or 30 min after drug treatment followed by determination of HOIfos in plasma by the two methods. Comparison of plasma levels of HOIfos determined by the two methods indicated only minor differences between the two. These results suggest the possibility that the nonspecific method may be acceptable as a first estimation of levels of this metabolite in biological fluids until the development of a specific method that does not require radiolabeled drug, such as high-performance liquid chromatography or gas chromatography/mass spectrometry, has been developed.