IFEX-ifosfamide injection, powder, for solution
BAXTER HEALTHCARE CORPORATION
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IFEX
(ifosfamide for injection, USP)
Rx Only
WARNING
IFEX should be administered under the supervision of a qualified physician experienced in the use of cancer chemotherapeutic agents. Urotoxic side effects, especially hemorrhagic cystitis, as well as CNS toxicities such as confusion and coma have been associated with the use of IFEX. When they occur, they may require cessation of IFEX therapy. Severe myelosuppression has been reported. (See ADVERSE REACTIONS section.)
DESCRIPTION
IFEX (ifosfamide for injection, USP) single-dose vials for constitution and administration by intravenous infusion each contain 1 gram or 3 grams of sterile ifosfamide. Ifosfamide is a chemotherapeutic agent chemically related to the nitrogen mustards and a synthetic analog of cyclophosphamide. Ifosfamide is 3-(2-chloroethyl)-2-[(2-chloroethyl)amino]tetrahydro-2H-1,3,2-oxazaphosphorine 2-oxide. The molecular formula is C7H15Cl2N2O2P and its molecular weight is 261.1. Its structural formula is: Ifosfamide is a white crystalline powder that is soluble in water.
CLINICAL PHARMACOLOGY
Ifosfamide has been shown to require metabolic activation by microsomal liver enzymes to produce biologically active metabolites. Activation occurs by hydroxylation at the ring carbon atom 4 to form the unstable intermediate 4-hydroxyifosfamide. This metabolite rapidly degrades to the stable urinary metabolite 4-ketoifosfamide. Opening of the ring results in formation of the stable urinary metabolite, 4-carboxyifosfamide. These urinary metabolites have not been found to be cytotoxic. N, N-bis (2-chloroethyl)-phosphoric acid diamide (ifosphoramide) and acrolein are also found. Enzymatic oxidation of the chloroethyl side chains and subsequent dealkylation produces the major urinary metabolites, dechloroethyl ifosfamide and dechloroethyl cyclophosphamide. The alkylated metabolites of ifosfamide have been shown to interact with DNA.
In vitro incubation of DNA with activated ifosfamide has produced phosphotriesters. The treatment of intact cell nuclei may also result in the formation of DNA-DNA cross-links. DNA repair most likely occurs in G-1 and G-2 stage cells.
Pharmacokinetics
Ifosfamide exhibits dose-dependent pharmacokinetics in humans. At single doses of 3.8-5.0 g/m2, the plasma concentrations decay biphasically and the mean terminal elimination half-life is about 15 hours. At doses of 1.6-2.4 g/m2/day, the plasma decay is monoexponential and the terminal elimination half-life is about 7 hours.
Ifosfamide is extensively metabolized in humans and the metabolic pathways appear to be saturated at high doses.
After administration of doses of 5 g/m2 of 14C-labeled ifosfamide, from 70% to 86% of the dosed radioactivity was recovered in the urine, with about 61% of the dose excreted as parent compound. At doses of 1.6-2.4 g/m2 only 12% to 18% of the dose was excreted in the urine as unchanged drug within 72 hours.
Two different dechloroethylated derivatives of ifosfamide, 4-carboxyifosfamide, thiodiacetic acid and cysteine conjugates of chloroacetic acid have been identified as the major urinary metabolites of ifosfamide in humans and only small amounts of 4-hydroxyifosfamide and acrolein are present. Small quantities (nmole/mL) of ifosfamide mustard and 4-hydroxyifosfamide are detectable in human plasma. Metabolism of ifosfamide is r |
