Plasma Concentrations Of Cyclophosphamide Research Articles

Fractionated oral dosing and its effect on cyclophosphamide pharmacokinetics in dogs with high-grade multicentric lymphoma.

Cyclophosphamide (CP) is an alkylating agent commonly included in multi-drug treatment protocols for canine cancer. As a prodrug, CP requires hepatic metabolism for activation to the intermediate compound 4-hydroxycyclophosphamide (4-OHCP) which then spontaneously forms alkylating phosphoramide mustard. CP is frequently administered in a fractionated manner, with the total dose given over multiple days. CP is reported to cause auto-induction of metabolism in humans, with faster CP clearance and relatively increased 4-OHCP formation following fractionated versus bolus dosing, however canine pharmacokinetic studies of CP dose fractionation are lacking. The study objective was to evaluate the pharmacokinetics of fractionated oral CP dosing at a dose of 200-250 mg/m2 over 3 to 4 days in a prospectively identified population of cancer-bearing dogs. Plasma concentrations of CP and 4-OHCP were measured by ultra-high performance liquid chromatography tandem-mass spectrometry in eight dogs following the first and last doses to assess for auto-induction of CP metabolism. No significant difference in the rate of CP elimination between first and last doses were detected (0.73 ± 0.46 vs. 1.22 ± 0.5h-1 ; p=.125). Additionally, no significant difference in dose-normalized 4-OHCP exposure was identified between first and last doses (5.9 ± 2.1 vs. 7.9 ± 6.4h × ng/ml; p=.936). These results suggest that fractionated dosing may not increase exposure to the active metabolite of CP in dogs as it does in humans. As such, standard bolus dosing and fractionated dosing may be equivalent in terms of bio-activation of CP in dogs administered a dose of 200-250 mg/m2 .

Effects of triptolide on the pharmacokinetics of cyclophosphamide in rats: A possible role of CytochromeP3A4 inhibition

To evaluate the effect of a 10-day course of triptolide (TP) on rat cytochrome (CY) P3A4 activity, and on the pharmacokinetics of cyclophosphamide (CPA). In the pharmacokinetics experiment, rats were orally given 0.9% NaCl solution (n=5) and TP [1.2 (mg/kg·d)] for 10 days and a single dose of CPA was administered intravenously (100 mg/kg) to rats on day 11. Blood samples were collected up to 4 h at predetermined time intervals, the plasma concentration of CPA was determined by high performance liquid chromatography (HPLC) and pharmacokinetic parameters were determined. In the in vitro CYP3A4 activity inhibition research, rat blank liver microsomes were divided into 3 groups: a control group, a TS (5 μL, 200 μmol/L) with TP (5 μL, 12.5 μmol/L) group, a TS with ketoconazole (5 μL, 1 μmol/L) group. Concentration of 6β-hydroxylated testosterone (6β-OHT) in liver microsomes was measured by HPLC and the activity of CYP 3A4 was calculated through the following formula: Einhibitor/Econtrol × 100%=Cinhibitor/Ccontrol × 100%. Compared with the control group, the area under the plasma concentration-time curve (AUC0-∞) of CPA was significantly increased by 229.05% pretreated with TP (P<0.01). Peak plasma concentrations (Cmax) of CPA was significantly increased and plasma half-life was correspondingly extended. The CYP3A4 activity was significantly inhibited by ketoconazole 93.5%±0.2% and TP 84.6%±0.3% compared with the control group (P<0.01 and P<0.05, respectively). Our results strongly suggested that long-term oral intake of TP can distinctly inhibit the CYP3A4 activity and this inhibition evidently decrease the formation of toxic metabolites of CPA.

Investigating the pharmacokinetics and dosing of anticancer drugs in infants and young children.

10033 Background: Dosing regimens for anticancer drugs administered to infants and young children frequently differ between tumour types and protocols, with dosing based on body weight commonly implicated. We have recently highlighted a reduced exposure to 13-cis-retinoic acid in neuroblastoma patients &lt;12kg dosed on body weight (Clin Cancer Res19:469-79,2013). Given the toxicity observed with many chemotherapeutics, it is appropriate to establish a pharmacological basis for dose adjustments implemented in younger patients. Methods: The pharmacokinetics of cyclophosphamide (CPA), actinomycin D (Act D), carboplatin and etoposide were investigated in children aged 0-6, 6-12 and 12-24 months. CPA was administered i.v. at a dose of 100-1,500 mg/m2, with infusion times up to 1.5h, Act D as a bolus i.v. infusion of 0.4-1.5mg/m2, carboplatin as an i.v. dose of 3.8-30mg/kg over 1-4h and etoposide as an i.v. dose of 3.5-14mg/kg over 1-6h. Eighty-six children were studied at 14 centres, with PK sampling carried out over 24h for CPA and Act D, 3h for carboplatin and up to 6h for etoposide. Plasma concentrations of CPA, Act D and etoposide were determined by LC-MS analysis, with carboplatin concentrations determined in plasma ultrafiltrate by AAS. PK parameters were calculated using WinNonlin or previously used PK models as appropriate. Results: Clearance values normalized to body weight ranged from 0.5-7.7 ml/min/kg for CPA, 1.7-17.4 for Act D, 1.6-10.5 for carboplatin and 0.2-1.7 for etoposide. No significant differences in normalized clearance were observed between the defined age cohorts of 0-6, 6-12 and 12-24 months and the data do not indicate clear differences in drug handling in infants and young children. However, when normalized clearance values were compared to data from older children, a greater degree of inter-patient variation was observed in patients &lt;2 years than in children &gt;2 years for all drugs. Conclusions: While normalized clearance values for the drugs studied do not support reduced dosing approaches, data suggest that individual drug clearance values may be more difficult to predict in younger patients. Further studies involving additional anticancer drugs may allow more rationale approaches to dosing. Clinical trial information: NCT00897871.

Pharmacokinetics of cyclophosphamide and its metabolites in paediatric patients receiving high-dose myeloablative therapy

IntroductionIn order to better understand the impact of high-dose on the pharmacokinetics and metabolism of cyclophosphamide, a pharmacological study was performed in children with malignant mesenchymal tumours with metastatic disease. MethodsPatients received four courses of chemotherapy including two courses of cyclophosphamide. Plasma concentrations of cyclophosphamide and the metabolites 4-ketocyclophosphamide, dechloroethylcyclophosphamide and carboxyphosphamide were determined on days 1, 2 and 3 of each course. A population pharmacokinetic model for cyclophosphamide was developed using non-linear mixed effects modelling and metabolite AUC values were compared between days and courses. ResultsData were available on 21 cyclophosphamide courses from 15 patients. A one compartment model, incorporating a term in surface area for both CL and V, best described cyclophosphamide pharmacokinetics. Typical CL and V on day 1 of treatment for a patient with a SA of 1.4m2 were 4.3L/h and 28.5L, respectively. On days 2 and 3 CL increased by 88% (95% CI, 72–105%) and 125% (95% CI, 108–145%) over day 1 levels; V increased by 14% (95% CI, 5–23%) on days 2 and 3. V tended to be larger for males than similarly sized females but no effect of age was found upon CL or V. Significant increases in metabolite AUCs were observed on days 2 and 3 compared to day 1 and a significant increase in CXCP AUC from course 1 to course 3. ConclusionAdministration of high-dose cyclophosphamide over several days results in an increase in metabolism, possibly by induction of the activation pathway. This induction is effectively reversed following a four week period between cyclophosphamide doses. The degree of intersubject variation in cyclophosphamide elimination is largely accounted for by body surface area and is less than previously reported.

Simultaneous determination of cyclophosphamide and 4-hydroxycyclophosphamide in human plasma by high-performance liquid chromatography coupled with electrospray ionization tandem mass spectrometry – application to Chinese systemic lupus erythematosus patients

A pharmacogenomics study of cyclophosphamide in systemic lupus erythematosus patients is being conducted in our laboratory in which the plasma concentrations of cyclophosphamide and its active metabolite 4-hydroxycyclophosphamide should be assayed rapidly and sensitively. A rapid, stable and sensitive liquid chromato-graphy/electrospray ionization tandem mass spectrometry method was developed to simultaneously determine cyclophosphamide and 4-hydroxycyclophosphamide in human plasma with ifosfomide as an internal standard. After a protein precipitation with cold acetonitrile and stabilization of 4-hydroxycyclophosphamide by ansyldrazine and extraction with ethyl acetate, separation was performed on a C18 3.5 μm 2.1 × 50 mm column with mobile phase of acetonitrile and water (50:50, v/v) with 0.1% formic acid at 200 μL/min. The chromatographic run time was 3 min. The linear calibration curves ranged from 5 to 5000 ng/mL for cyclophosphamide and 5-500 ng/mL for 4-hydroxycyclophosphamide. The recoveries of the liquid extraction were 54.5%-58.5% for cyclophosphamide and 103.5%-105.5% for 4-hydroxycyclophosphamide. The lower limit of quantification was 5 ng/mL for both analytes. The intra- and inter-day precision was <15% for quality control samples at 4000, 500, 50 ng/mL for cyclophosphamide and 4-hydroxycyclophosphamide at 400, 100, 20 ng/mL. The method was applied in this pharmacogenomics study in Chinese systemic lupus erythematosus patients treated with low-dose cyclophosphamide. The method was efficient with shorter running time and lower limit of quantification compared to previous reports and has been successfully applied in this pharmacogenomics study.

Pharmacokinetics of Cyclophosphamide and Thiotepa in a Conventional Fractionated High-Dose Regimen Compared With a Novel Simplified Unfractionated Regimen

High-dose alkylating chemotherapy with cyclophosphamide (4000 or 6000 mg/m2) and thiotepa (320 or 480 mg/m2) has commonly been administered in a fractionated regimen over 4 days. A simplified unfractionated regimen would be preferable, especially because cyclophosphamide and thiotepa have been shown to influence the metabolism of each other. However, altering a dose regimen can have a profound effect on the pharmacokinetics of the compounds involved. The aim of this study was to investigate the effect of altering the fractionated administration schedule of the CTC regimen on cyclophosphamide and thiotepa pharmacokinetics. Plasma samples were collected from 124 patients who received a fractionated tiny CTC or CTC regimen of cyclophosphamide (1000 or 1500 mg m(-2) d(-1)), thiotepa (40 or 60 mg/m2 twice daily), and carboplatin (267 or 400 mg m(-2) day(-1)) for 4 days, and 16 patients who received an unfractionated mini CTC regimen of cyclophosphamide (3000 mg/m2 at day 1), carboplatin (400 mg/m2 at days 1 and 2), and thiotepa (250 mg/m2 at day 2). Plasma concentrations of cyclophosphamide and 4-hydroxycyclophosphamide were determined using high-performance liquid chromatography coupled with tandem mass spectrometric detection; plasma concentrations of thiotepa and tepa were determined using gas chromatography. Pharmacokinetics of cyclophosphamide and thiotepa were assessed using nonlinear mixed-effect modeling. The study showed that alteration of a fractionated high-dose regimen into a simplified unfractionated regimen resulted in saturation of thiotepa elimination, with a Vmax of 212 (+/-58) micromol/h and a Km of 13.7 (+/-5.9) microM. This resulted in an increased dose-corrected exposure to thiotepa (13%) and decreased dose-corrected exposure to its metabolite tepa (21%). Elimination of cyclophosphamide was not shown to be saturable. Dose-corrected exposures to cyclophosphamide and its active metabolite 4-hydroxycyclophosphamide were comparable in both regimens. Because the simplified unfractionated mini CTC regimen was more patient-friendly and because overall dose-corrected exposures to cyclophosphamide and thiotepa were not affected to a relevant extent, our data suggest that this unfractionated regimen can be used safely in future studies.

Genetic polymorphisms of CYP2B6 affect the pharmacokinetics/pharmacodynamics of cyclophosphamide in Japanese cancer patients

To evaluate the effects of genetic polymorphisms of drug metabolizing enzymes on the pharmacokinetics of cyclophosphamide and its active metabolite, 4-hydroxycyclophosphamide, and on the pharmacodynamics. One hundred and three Japanese patients with malignant lymphoma or breast cancer treated with cyclophosphamide (500-750 mg/m) participated in this study. The plasma concentrations of cyclophosphamide and 4-hydroxycyclophosphamide were determined by high-performance liquid chromatography, and pharmacokinetic parameters were calculated. The genotypes of CYP2B6, CYP2C19, CYP3A4, CYP3A5, ALDH1A1, GST genes were determined by allele-specific polymerase chain reaction or polymerase chain reaction-restriction-fragment length polymorphism. A large interindividual difference (54-fold) was observed in the area under the curve ratio of 4-hydroxycyclophosphamide/cyclophosphamide calculated as the metabolic index. We first proved that leukocytopenia and neutropenia were significantly (P<0.01) related to the area under the curve of 4-hydroxycyclophosphamide. We found that the homozygotes of CYP2B6*6 (Q172H and K262R) showed significantly (P<0.05) higher clearance and shorter half-life of cyclophosphamide than heterozygotes and homozygotes of CYP2B6*1. The small sample size, however, limited the impact. On the other hand, it was clearly demonstrated that the patients possessing the single nucleotide polymorphisms of the CYP2B6 gene, g.-2320T>C, g.-750T>C (5'-flanking region), g.15582C>T (intron 3), or g.18492T>C (intron 5), had significantly lower area under the curve ratios of 4-hydroxycyclophosphamide/cyclophosphamide, indicating a decreased cyclophosphamide 4-hydroxylation. Of particular importance was the finding that leukocytopenia was significantly related to the single nucleotide polymorphisms g.-2320T>C, g.-750T>C, and g.18492T>C in CYP2B6 gene, which are highly linked. No relationship was observed between the pharmacokinetics of cyclophosphamide or 4-hydroxycyclophosphamide and genetic polymorphisms of the other enzymes. We clarified that the single nucleotide polymorphisms in the promoter region or introns in the CYP2B6 affect the potency of cyclophosphamide activation to 4-hydroxycyclophosphamide. This information would be valuable for predicting adverse reactions and the clinical efficacy of cyclophosphamide.

Pharmacokinetics of N-2-chloroethylaziridine, a volatile cytotoxic metabolite of cyclophosphamide, in the rat

The objectives of this study were to characterize pharmacokinetics of N-2-chloroethylaziridine (CEA) in the rat model and assess the in vivo fraction of total clearance of phosphoramide mustard (PM) that furnished CEA to circulation. The disposition of CEA was investigated following separate intravenous (iv) administrations of PM, synthetic CEA, and their combination to the Sprague-Dawley rats. In addition, in rats receiving prodrug cyclophosphamide (CP), plasma concentrations of CP and its metabolites, 4-hydroxycyclophosphamide (HOCP), PM, and CEA, were simultaneously quantified using GC/MS and stable isotope dilution techniques. Following iv administration of synthetic CEA, concentrations of CEA declined biexponentially with the mean terminal half-life and total body clearance of 47.5 min and 167 ml/min/kg, respectively. Urinary excretion of unchanged CEA was 0.164% of the administered dose. CEA was found to be the major circulating metabolite after iv administration of precursor PM to rats. The fraction of total clearance of PM that furnished CEA to circulation was estimated to be 100%, indicating virtually complete availability of the metabolite to circulation once formed. In rats administered with CP, PM exhibited the highest plasma and urinary concentrations compared to HOCP and CEA. For the first time, CEA was demonstrated to be an important in vivo metabolite of CP in the present study. In light of the poor permeability and in vivo stability of PM, the ultimate DNA alkylator, the findings obtained in this study suggested that CEA may contribute significantly to the overall antitumor activity of prodrug CP.

Dose escalation of cyclophosphamide in patients with breast cancer: consequences for pharmacokinetics and metabolism.

The alkylating anticancer agent cyclophosphamide (CP) is a prodrug that undergoes a complex metabolism in humans producing both active and inactive metabolites. In parallel, unchanged CP is excreted via the kidneys. The aim of this study was to investigate the influence of dose escalation on CP pharmacokinetics and relative contribution of activating and inactivating elimination pathways. Pharmacokinetics of CP were assessed in 12 patients with high-risk primary breast cancer who received an adjuvant chemotherapy regimen that included four courses of conventional-dose CP (500 mg/m2 over 1 hour every 3 weeks) followed by one final course of high-dose CP (100 mg/kg over 1 hour). Plasma concentrations of CP were analyzed by high-performance liquid chromatography (HPLC), 24-hour urinary concentrations of CP, and its inactive metabolites (carboxyphosphamide, dechloroethylcyclophosphamide [dechlorethylCP], ketocyclophosphamide [ketoCP]) were determined by 31-phosphorus-nuclear magnetic resonance (31P-NMR)-spectroscopy. There was no difference in dose-corrected area under the concentration-time curve (AUC) (216 v 223 [mumol.h/[mL.g]), elimination half-life (4.8 v 4.8 hours), systemic clearance (79 v 77 mL/min) and volume of distribution (0.49 v 0.45 L/kg) of CP between conventional- and high-dose therapy, respectively. However, during high-dose chemotherapy, we observed a significant increase in the renal clearance of CP (15 v 23 mL/min; P < .01) and in the formation clearance of carboxyphosphamide (7 v 12 mL/min; P < .05) and dechloroethylCP (3.2 v 4.2 mL/min; P < .05), whereas metabolic clearance to ketoCP remained unchanged (1.3 v 1.2 mL/min). Consequently, metabolic clearance to the remaining (reactive) metabolites decreased from 52 to 38 mL/min (P < .001). The relative contribution of the different elimination pathways to overall clearance of CP demonstrated wide interindividual variability. Overall pharmacokinetics of CP are apparently not affected during eightfold dose escalation. However, there is a shift in the relative contribution of different clearances to systemic CP clearance in favor of inactivating elimination pathways, thereby indicating saturation of bioactivating enzymes during dose escalation. Besides individual enzyme capacity, hydration and concomitant medication with dexamethasone modulated CP disposition.