THE PHARMACOKINETICS OF IFOSFAMIDE GIVEN AS SHORT AND LONG INTRAVENOUS INFUSIONS IN CANCER-PATIENTS

1 We investigated the pharmacokinetics of ifosfamide 5 g m-2 given by two regimens. Six patients (one female), median age 55 (range 40-71) years, all with lung cancer received 5 g m-2 ifosfamide (median ifosfamide dose 8.95 g) as an intravenous infusion over 0.5 h with mesna. Four other cancer patients (all male) of median age 52.5 (range 23-72) years were studied on seven treatment occasions with 5 g m-2 ifosfamide (median ifosfamide dose 8.88 g) as a 24 h intravenous infusion with mesna. Plasma was assayed for ifosfamide by gas liquid chromatography and for alkylating activity by the nitrobenzylpyridine method. 2 After ifosfamide 5 g m-2 infused over 0.5 h, the decay of the plasma ifosfamide concentration was monoexponential with a median (range) t1/2,z of 5.4 h (3.6-10.4 h). The median clearance was 60 ml min-1 (47-104) and the median volume of distribution was 388 (329-783) ml kg-1. Plasma nitrobenzylpyridine alkylating activity showed a biexponential decay in four patients and a monoexponential decay in two, with a median AUC of 102 (24-177) nmol nor nitrogen mustard eq h ml-1. 3 When ifosfamide 5 g m-2 was given as a 24 h infusion, the decay of the plasma ifosfamide concentration was monoexponential, the median (range) t1/2,z was 4.5 (3.4-6.1), the median volume of distribution was 563 (292-818) ml kg-1 and the median clearance was 79 (59-116) ml min-1. Plasma nitrobenzylpyridine alkylating activity decayed monoexponentially and the median AUC was 49 (45-131) nmol nor nitrogen mustard eq ml-1 h. 4 There was no evidence of saturation kinetics after high doses of ifosfamide. The clearance of ifosfamide at 5 g m-2 was similar whether it was given by short or 24 h intravenous infusion and was comparable with that observed after low doses of ifosfamide.