Influence of dose and infusion duration on pharmacokinetics of ifosfamide and metabolites

The anticancer drug ifosfamide is a prodrug requiring activation through 4-hydroxyifosfamide to ifosforamide mustard, to exert cytotoxicity. Deactivation of ifosfamide leads to 2- and 3-dechloroethylifosfamide and the release of potentially neurotoxic chloracetaldehyde. The aim of this study was to quantify and to compare the pharmacokinetics of ifosfamide, 2- and 3-dechloroethylifosfamide, 4-hydroxyifosfamide, and ifosforamide mustard in short (1-4 h), medium (24-72 h), and long infusion durations (96-240 h) of ifosfamide. An integrated population pharmacokinetic model was used to describe the autoinducible pharmacokinetics of ifosfamide and its four metabolites in 56 patients. The rate by which autoinduction of the metabolism of ifosfamide developed was found to be significantly dependent on the infusion schedule. The rate was 52% lower with long infusion durations compared with short infusion durations. This difference was, however, comparable with its interindividual variability (22%) and was, therefore, considered to be of minor clinical importance. Autoinduction caused a less than proportional increase in the area under the ifosfamide plasma concentration-time curve (AUC) and more than proportional increase in metabolite exposure with increasing ifosfamide dose. During long infusion durations dose-corrected exposures (AUC/D) were significantly decreased for ifosfamide and increased for 3-dechloroethylifosfamide compared with short infusion durations. No differences in dose-normalized exposure to ifosfamide and metabolites were observed between short and medium infusion durations. This study demonstrates that the duration of ifosfamide infusion influences the exposure to the parent and its metabolite 3-dechloroethylifosfamide. The observed dose and infusion duration dependence should be taken into account when modeling ifosfamide metabolism.

Pharmacokinetics of ifosfamide and some metabolites in children

The pharmacokinetics of ifosfamide and some metabolites in children was investigated. The patients received various doses of ifosfamide, mostly by continuous infusion, over several days. The penetration of ifosfamide and its metabolites into the cerebrospinal fluid was also studied in four cases. Ifosfamide and 4-hydroxyifosfamide pass the blood-brain barrier, reaching cerebrospinal fluid concentrations that are almost as high as plasma concentrations.

Chromatographic analysis of the enantiomers of ifosfamide and some of its metabolites in plasma and urine

The enantiomers of the cytostatic drug ifosfamide and the two metabolites 2- and 3-dechloroethylifosfamide were isolated from plasma and urine by liquid-liquid extraction with ethyl acetate, resolved on a Chirasil-L-val gas chromatographic column and detected by a nitrogen-phosphorus-selective flame ionisation detector. Resolution of the racemic compounds for identification purposes was also accomplished with high-performance liquid chromatography on a chiral column. The validated gas chromatographic method was suitable to determine the total concentrations and the enantiomeric composition of ifosfamide and its dechloroethylated metabolites in plasma and urine samples from treated patients. Some metabolic preferences in the metabolism of ifosfamide were found.

Determination of 4-hydroxyifosfamide in biological matrices by high-performance liquid chromatography

A high-performance liquid chromatographic method has been developed for the determination of 4-hydroxyifosfamide, a metabolite of ifosfamide, in plasma of cancer patients. The analyte is derivatized to 7-hydroxyquinoline, which can be detached fluorimetrically. The calibration graph is linear in the concentration range 0.05-25 microM, the limit of detection being 40 nM. Any inference from acrolein, another metabolite of ifosfamide, was ruled out. 4-Hydroxyifosfamide is very unstable in plasma and a stabilization procedure by adding citric acid has been developed. Thus treated, the samples were stable for 4 days. Analysis of a patient's plasma samples revealed that the 4-hydroxifosfamide concentration did not exceed 10 microM.

Analysis of ifosforamide mustard, the active metabolite of ifosfamide, in plasma

Ifosforamide mustard is the active metabolite of ifosfamide, a cytostatic drug. In this study a sensitive and selective method for the analysis of ifosforamide mustard in plasma is described. The method consists of direct derivatisation of ifosforamide mustard in plasma with diethyldithiocarbamate and subsequent solid-phase extraction of the resulting derivative. The analysis of the derivatisation product was performed by high-performance liquid chromatography with UV detection. The calibration graph was linear in the concentration range 0.45-45 microM and the minimum detectable concentration was 0.45 mumol. The samples were stabilised by addition of semicarbazide and sodium chloride. A patient's plasma sample was analysed by means of the described method. The ifosforamide mustard concentration was 2.3 microM.

Pharmacokinetics of ifosfamide, 2- and 3-dechloroethylifosfamide in plasma and urine of cancer patients treated with a 10-day continuous infusion of ifosfamide

The cytotoxic drug ifosfamide is subject to an extensive metabolism. This study reports the results of a pharmacokinetic study of the parent drug and the two dechloroethylated metabolites in 22 patients on a 10-day continuous infusion of ifosfamide. Ifosfamide causes a substantial induction of the enzymes responsible for its metabolism, resulting in a two-fold increase of the clearance. The maximal IF concentration is reached after 24 h, after which the concentration decreases to a steady-state. The dechloro-ethylated compounds can be detected in the plasma about 8 h after the start of the infusion with plasma half-lives longer than for IF. Urinary excretion studies revealed that at least a quarter of the IF dose is excreted as inactive compounds.

Ifosfamide metabolism and pharmacokinetics (review)

In this article the studies on the pharmacokinetics and metabolism of ifosfamide have been summarised. Ifosfamide is a pro-drug and requires metabolic activation to exert cytotoxic activity. The various metabolites determined after oral or intravenous administration of ifosfamide show a large inter- and intrapatient variability. Oral and intravenous fractionated treatment with ifosfamide exhibits a time-dependent increase in ifosfamide metabolic clearance which is explained by a mechanism of auto-induction of the hepatic oxygenase system. The pharmacokinetic parameters of ifosfamide do not correlate with age, sex and weight. Oral ifosfamide, at a dose higher than 1 g/m2, induces neurotoxicity in a high percentage of patients. In these cases the pharmacokinetics of ifosfamide were not aberrant. This implies that ifosfamide metabolites rather than the parent drug are likely to be responsible for the neurotoxicity. The development of more selective and sensitive analytical methodologies are necessary in order to go in more insight into the disposition of the active ifosfamide metabolites, including their clinical effects. This may lead to a further optimisation of the therapeutic use of ifosfamide.

The analysis of ifosfamide and its metabolites (review)

Ifosfamide is a member of the oxazaphosphorine class of cytostatic drugs. Ifosfamide has to be metabolized prior to expressing its cytotoxicity. This metabolism leads to a great variety of metabolites. An overview is given of the methods of analysis of ifosfamide and its metabolites as well as the current knowledge about its metabolism, toxicity and clinical use in relation to the bio-analysis. For ifosfamide and some of its metabolites reliable methods of analysis exist. However, for the most important metabolites, isofosforamide mustard and acrolein, progress has to be made in improving the simplicity and sensitivity of the existing methods.

Determination of chloroacetaldehyde, a metabolite of oxazaphosphorine cytostatic drugs, in plasma

A derivatization high-performance liquid chromatographic method with ultraviolet detection to monitor the plasma concentration of chloroacetaldehyde, a neurotoxic metabolite of oxazaphosphorine drugs, is presented. To prevent the rapid degradation of chloroacetaldehyde, the plasma samples are stabilized with formaldehyde. The method is linear in the concentration range 1-250 nmol/ml. Blood samples from a patient who was treated with a ten-day continuous infusion of ifosfamide were assayed. The chloroacetaldehyde concentrations did not exceed 10 nmol/ml.

Gas chromatographic determination of 2- and 3-dechloroethylifosfamide in plasma and urine

The metabolic oxidation of one of the chloroethyl groups of the antitumour drug ifosfamide leads to the formation of the inactive metabolites 2- and 3-dechloroethylifosfamide together with the neurotoxic metabolite chloroacetaldehyde. A very sensitive capillary gas chromatographic method, requiring only 50 microliters of plasma or urine, has been developed to measure the amounts of the drug and the two inactive metabolites in a single run. Calibration curves were linear (r > 0.999) in the concentration ranges from 50 ng/ml to 100 micrograms/ml in plasma and from 100 ng/ml to 1 mg/ml in urine.

Chemical stability of two sterile, parenteral formulations of cyclophosphamide (Endoxan) after reconstitution and dilution in commonly used infusion fluids

The commercially available parenteral dosage forms of cyclophosphamide (Endoxan, Cycloblastine) are manufactured by an aseptic dry-filling technique and exhibit a slow dissolution rate. A novel dosage form has been developed by one of the manufacturers based on the technique of freeze drying. Dissolution rates of both types of formulations were determined and it was shown that the freeze-dried formulation dissolves more rapidly, within 20 seconds, while it takes at least three minutes to dissolve the dry-filled formulation. The chemical stabilities of the cyclophosphamide solutions, obtained after reconstitution and/or dilution of both formulations, have been investigated and tested as a function of drug concentration (20 and 1 mg/mL), solvent (water, 0.9% sodium chloride, 5% dextrose), container material (glass and polyvinyl chloride (PVC)), light conditions (normal room fluorescent light/dark) and temperature (4 degrees, 20-22 degrees and 37 degrees C). The test solutions were analyzed by a stability-indicating reverse phase high performance liquid chromatographic method with ultraviolet detection at 214 nm. Cyclophosphamide solutions (solvent: water; drug concentration; 20 mg/mL) are stable when stored for seven days at 4 degrees C in the dark. At higher temperatures degradation occurred during the test period with 10% loss after seven days at ambient temperature and 50% loss after seven days storage at 37 degrees C. Similar data were found in admixtures with 5% dextrose and 0.9% sodium chloride and initial drug concentration of 1 mg/mL. There are no significant differences in chemical stability between the solutions obtained from reconstitution and dilution of the dry-filled and lyophilized formulations.(ABSTRACT TRUNCATED AT 250 WORDS)

Gas chromatographic determination of ifosfamide in microvolumes of urine and plasma

In oncology, particularly in pediatric malignancies, high doses (5-10 g/m2) of the oxazaphosphorine ifosfamide play an important role in the treatment of sarcomas. Pharmacokinetic data of ifosfamide and its metabolites in these cases are scanty. Considering the special demands of the determination of ifosfamide in plasma of young children, a very sensitive capillary gas chromatographic method, requiring only 50 microliters of plasma, has been developed. This bioanalysis of ifosfamide shows good linearity and accuracy in the concentration range 10 ng to 100 micrograms per ml of plasma and 25 ng to 1 mg per ml of urine. The absolute limits of detection in plasma and urine are 2 ng/ml and 5 ng/ml, respectively. The stability of various solutions of ifosfamide and trofosfamide was tested and proved to be satisfactory, except for ifosfamide in plasma and urine kept in the refrigerator. The validity of the method for pharmacokinetic purposes is shown in the case of one patient.

A systematic study on the chemical stability of ifosfamide

The degradation kinetics of ifosfamide in aqueous solution have been investigated over the pH region 1-13 at 70 degrees C. A stability indicating high-performance liquid chromatographic assay with UV detection was used to separate degradation products from the parent compound. The degradation kinetics were studied as related to pH, buffer composition, ionic strength, temperature and drug concentration. A pH-rate profile at 70 degrees C, obtained from (pseudo) first-order kinetic plots, was constructed after corrections for buffer effects were made. The degradation reactions of ifosfamide were found to be largely independent of pH, although proton or hydroxyl catalysis occurs at extreme pH values. Ifosfamide shows maximum stability in the pH region 4-9, corresponding to a half-life of 20 h.

The risks of handling cytotoxic drugs. II. Recommendations for working with cytotoxic drugs

Presuming that preparation of antineoplastic drugs without proper protection may lead to mutagenic urine (of which the effects are uncertain), one has to take great care when preparing these drugs. Apart from Norway no other country has national regulations issued by the government for handling cytostatic agents. Many organizations in various countries have made their own guidelines, which may be adapted to the situations in local hospitals. The following recommendations have been compiled after a review of the literature. They reflect a personal set of guidelines for preparation, administration and disposal of cytotoxic drugs. They are probably the minimum precautions that should be taken, and have not been approved by any committee or agency. Further precautions must first have their potential benefit weighed against probable inconvenience and additional costs.

The risks of handling cytotoxic drugs. I. Methods of testing exposure

Results of various biological and physical/chemical tests of the urines or blood of health-care personnel working with cytotoxic drugs are discussed. The outcomes of these tests are conflicting and inconclusive. The physical/chemical tests seem to be an alternative method. However, until now it has not been possible to establish the threshold concentration in urine or blood beneath which no effect has to be expected. Therefore, the interpretation of the concentration of cytotoxic drugs and/or the metabolites in the urine or blood is difficult. As long as one will not be able to provide conclusive data on the health hazards when working with cytotoxic drugs, protective measures have to be taken in order to lower the risk as much as possible.