Intramolecular rearrangement of ifosfamide in aqueous solutions

Ifosfamide - History, efficacy, toxicity and encephalopathy

In this review we trace the passage of fundamental ideas through 20^th century cancer research that began with observations on mustard gas toxicity in World War I. The transmutation of these ideas across scientific and national boundaries, was channeled from chemical carcinogenesis labs in London via Yale and Chicago, then ultimately to the pharmaceutical industry in Bielefeld, Germany. These first efforts to checkmate cancer with chemicals led eventually to the creation of one of the most successful groups of cancer chemotherapeutic drugs, the oxazaphosphorines, first cyclophosphamide (CP) in 1958 and soon thereafter its isomer ifosfamide (IFO). The giant contributions of Professor Sir Alexander Haddow, Dr. Alfred Z. Gilman & Dr. Louis S. Goodman, Dr. George Gomori and Dr. Norbert Brock step by step led to this breakthrough in cancer chemotherapy. A developing understanding of the metabolic disposition of ifosfamide directed efforts to ameliorate its side-effects, in particular, ifosfamide-induced encephalopathy (IIE). This has resulted in several candidates for the encephalopathic metabolite, including 2-chloroacetaldehyde, 2-chloroacetic acid, acrolein, 3-hydroxypropionic acid and S-carboxymethyl-L-cysteine. The pros and cons for each of these, together with other IFO metabolites, are discussed in detail. It is concluded that IFO produces encephalopathy in susceptible patients, but CP does not, by a "perfect storm," involving all of these five metabolites. Methylene blue (MB) administration appears to be generally effective in the prevention and treatment of IIE, in all probability by the inhibition of monoamine oxidase in brain potentiating serotonin levels that modulate the effects of IFO on GABAergic and glutamatergic systems. This review represents the authors' analysis of a large body of published research.

Prophylaxis and reversal of ifosfamide encephalopathy with methylene-blue

The antineoplastic ifosfamide produces dose-dependent signs of neurotoxicity. After ifosfamide overdose in a patient, we found excessive urinary excretion of glutaric acid and sarcosine, which is compatible with glutaric aciduria type II, a defect in mitochondrial fatty acid oxidation that results from defective electron transfer to flavoproteins. We therefore used the electron-accepting drug methylene-blue as an antidote for ifosfamide encephalopathy. In one patient, ifosfamide neurotoxicity was rapidly reversed by methylene-blue 50 mg intravenously. In another patient with previous episodes of ifosfamide encephalopathy, methylene-blue was administered orally prophylactically. No symptoms of neurotoxicity were noted.

Metabolism and pharmacokinetics of oral and intravenous ifosfamide

The initial metabolism of ifosfamide (IF) consists of two different pathways: enzymatic hydroxylation at carbon-4 forms the cytostatically active metabolite 4-OH-IF ("activated ifosfamide") whereas side-chain oxidation results in the liberation of chloroacetaldehyde, a compound with possible neurotoxic properties. The pharmacokinetics of ifosfamide and its activated form were investigated in 12 cancer patients, who received both oral and i.v. treatment in a randomized sequence on days 1 and 3 at a dose of 1 g/m2 (n = 7) or 1.5 g/m2 (n = 5). In 3 patients the pharmacokinetics of chloroacetaldehyde were also investigated. After oral application, ifosfamide absorption proceeded rapidly, the oral bioavailability was 0.92. Independent of the route of ifosfamide application on day 1, the terminal half-life on day 3 (when the drug was given by the alternative route) was decreased in 6 out of the 12 patients, thus indicating self-induction of hepatic metabolism. 4-OH-IF was already present 20 min after ifosfamide administration. In the individual patient the concentrations of 4-OH-IF were always higher after oral than after i.v. IF application: the mean p.o.:i.v. ratios for cmax and the area under the concentration/time curve were 2.3 and 1.7 respectively (P less than 0.05). In a first series of 3 patients the chloroacetaldehyde concentrations measured after oral ifosfamide application were about twice as high as those when the drug was given intravenously. These results indicate that (in comparison to the i.v. route) orally administered ifosfamide may be more cancerotoxic but also leads to higher levels of chloroacetaldehyde. This would explain the neurotoxic side-effects previously seen after oral administration of comparatively low ifosfamide doses.