Pharmacokinetics Of Cyclophosphamide Research Articles

Cytochrome P450 Oxidoreductase Influences CYP2B6 Activity in Cyclophosphamide Bioactivation.

IntroductionCyclophosphamide is commonly used as an important component in conditioning prior to hematopoietic stem cell transplantation, a curative treatment for several hematological diseases. Cyclophosphamide is a prodrug activated mainly by cytochrome P450 2B6 (CYP2B6) in the liver. A high degree of inter- and intra-individual variation in cyclophosphamide kinetics has been reported in several studies.Materials and MethodsHydroxylation of cyclophosphamide was investigated in vitro using three microsomal batches of CYP2B6*1 with different ratios of POR/CYP expression levels. Twenty patients undergoing hematopoietic stem cell transplantation were also included in the study. All patients received an i.v. infusion of cyclophosphamide (60 mg/kg/day, for two days) as a part of their conditioning. Blood samples were collected from each patient before cyclophosphamide infusion, 6 h after the first dose and before and 6 h after the second dose. POR gene expression was measured by mRNA analysis and the pharmacokinetics of cyclophosphamide and its active metabolite were determined.ResultsA strong correlation between the in vitro intrinsic clearance of cyclophosphamide and the POR/CYP ratio was found. The apparent K m for CYP2B6.1 was almost constant (3-4 mM), while the CLint values were proportional to the POR/CYP ratio (3-34 μL/min/nmol CYP). In patients, the average expression of the POR gene in blood was significantly (P <0.001) up-regulated after cyclophosphamide infusion, with high inter-individual variations and significant correlation with the concentration ratio of the active metabolite 4-hydroxy-cyclophosphamide/cyclophosphamide. Nine patients were carriers for POR*28; four patients had relatively high POR expression.ConclusionsThis investigation shows for the first time that POR besides CYP2B6 can influence cyclophosphamide metabolism. Our results indicate that not only CYPs are important, but also POR expression and/or activity may influence cyclophosphamide bioactivation, affecting therapeutic efficacy and treatment related toxicity and hence on clinical outcome. Thus, both POR and CYP genotype and expression levels may have to be taken into account when personalizing treatment schedules to achieve optimal therapeutic drug plasma concentrations of cyclophosphamide.

Combination of letrozole, metronomic cyclophosphamide and sorafenib is well-tolerated and shows activity in patients with primary breast cancer.

Purpose:To assess whether the combination of letrozole, metronomic cyclophosphamide and sorafenib (LCS) is well tolerated and shows activity in primary breast cancer (BC).Methods:Thirteen oestrogen receptor-positive, postmenopausal, T2-4, N0-1 BC patients received the LCS combination for 6 months. In these patients we examined the pharmacokinetics of sorafenib and cyclophosphamide, toxicity of the regimen, the clinical response to therapy and changes in the levels of biologically relevant biomarkers.Results:Adequate plasma concentrations of sorafenib were achieved in patients when it was dosed in combination with L+C. The mean plasma concentrations of C were consistently lower following administration of LCS, compared with administration of L+C only. The most common drug-related grade 3/4 adverse events were skin rash (69.3%), hand-foot skin reaction (69.3%) and diarrhoea (46.1%). According to RECIST Criteria, a clinical complete response was observed in 6 of 13 patients. A significant reduction in tumour size, evaluated with MRI, was also observed between baseline and 14 days of treatment in all 13 patients (P=0.005). A significant reduction in SUV uptake, measured by 18FDG-PET/CT, was observed in all patients between baseline and 30 days of treatment (P=0.015) and between baseline and definitive surgery (P=0.0002). Using modified CT Criteria, a response was demonstrated in 8 out of 10 evaluable patients at 30 days and in 11 out of 13 evaluable patients at the definitive surgery. A significant reduction in Ki67 expression was observed in all patients at day 14 compared with baseline (P<0.00001) and in 9 out of 13 patients at the definitive surgery compared with baseline (P<0.03). There was also a significant suppression of CD31 and VEGF-A expression in response to treatment (P=0.01 and P=0.007, respectively).Conclusions:The LCS combination is feasible and tolerable. The tumour response and target biomarker modulation indicate that the combination is clinically and biologically active.

Bioavailability of cyclophosphamide and vincristine after intraperitoneal administration in cats.

Cyclophosphamide and vincristine are widely used intravenous chemotherapeutic agents in both human and veterinary oncology. Although intravenous administration of these chemotherapeutics is the gold standard in most treatment protocols, this route of administration has several disadvantages (e.g. long infusion times and risk of extravasation). Therefore, alternative routes have been explored in the past. Recently, good clinical results were achieved with intraperitoneal (i.p.) administration of cyclophosphamide and vincristine in cats. However, the bioavailability following i.p. administration of cyclophosphamide and vincristine providing proof of principle has not been investigated and is the focus of the present study. The pharmacokinetics of cyclophosphamide and vincristine after i.p. and intravenous administration was investigated in six cats in a cross-over study by analysis of plasma levels of cyclophosphamide and vincristine after simultaneously administration of 0.6 mg/m vincristine and 200 mg/m cyclophosphamide. The median bioavailability on i.p. administration was 76% for cyclophosphamide and 100% for vincristine. Median areas under the curve for i.p. and intravenous administration were 11.4 and 16.0 ng h/ml for cyclophosphamide and 16.7 and 16.5 ng h/ml for vincristine, respectively. No specific i.p. administration-related adverse events were observed after i.p. administration. The high bioavailability of both cyclophosphamide and vincristine after i.p. administration and the absence of specific i.p. administration-related side effects suggest that i.p. administration is a suitable route of systemic chemotherapy for both chemotherapeutics. These results are promising and may serve as a stepping stone for the investigation of the pharmacology, safety, and efficacy of i.p. administration of cyclophosphamide and vincristine in humans.

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.

Aprepitant does not alter prednisolone pharmacokinetics in patients treated with R-CHOP

Aprepitant, a neurokinin 1 receptor antagonist, is an effective antiemetic drug in the prevention of chemotherapy-induced nausea and vomiting. Aprepitant co-administration increases plasma concentrations of dexamethasone and methylprednisolone by inhibiting cytochrome P450 (CYP) 3A4 [1], whereas pharmacokinetics of cyclophosphamide, which is also metabolized by CYP enzymes including CYP3A4, is not significantly changed by aprepitant [2]. Thus, aprepitant co-administration provides different effects on pharmacokinetics of CYP substrates; however, it is unknown whether aprepitant affects pharmacokinetics of prednisolone, another CYP3A4 substrate.

A phase 1 trial of imatinib, bevacizumab, and metronomic cyclophosphamide in advanced colorectal cancer

Background:This phase 1 clinical trial was conducted to determine the safety, maximum-tolerated dose (MTD), and pharmacokinetics of imatinib, bevacizumab, and metronomic cyclophosphamide in patients with advanced colorectal cancer (CRC).Methods:Patients with refractory stage IV CRC were treated with bevacizumab 5 mg kg−1 i.v. every 2 weeks (fixed dose) plus oral cyclophosphamide q.d. and imatinib q.d. or b.i.d. in 28-day cycles with 3+3 dose escalation. Response was assessed every two cycles. Pharmacokinetics of imatinib and cyclophosphamide and circulating tumour, endothelial, and immune cell subsets were measured.Results:Thirty-five patients were enrolled. Maximum-tolerated doses were cyclophosphamide 50 mg q.d., imatinib 400 mg q.d., and bevacizumab 5 mg kg−1 i.v. every 2 weeks. Dose-limiting toxicities (DLTs) included nausea/vomiting, neutropaenia, hyponatraemia, fistula, and haematuria. The DLT window required expansion to 42 days (1.5 cycles) to capture delayed toxicities. Imatinib exposure increased insignificantly after adding cyclophosphamide. Seven patients (20%) experienced stable disease for >6 months. Circulating tumour, endothelial, or immune cells were not associated with progression-free survival.Conclusion:The combination of metronomic cyclophosphamide, imatinib, and bevacizumab is safe and tolerable without significant drug interactions. A subset of patients experienced prolonged stable disease independent of dose level.

Comparison of an assumption‐free Bayesian approach with Optimal Sampling Schedule to a maximum a posteriori Approach for Personalizing Cyclophosphamide Dosing

Variable metabolism, dose-dependent efficacy, and a narrow therapeutic target of cyclophosphamide (CY) suggest that dosing based on individual pharmacokinetics (PK) will improve efficacy and minimize toxicity. Real-time individualized CY dose adjustment was previously explored using a maximum a posteriori (MAP) approach based on a five serum-PK sampling in patients with hematologic malignancy undergoing stem cell transplantation. The MAP approach resulted in an improved toxicity profile without sacrificing efficacy. However, extensive PK sampling is costly and not generally applicable in the clinic. We hypothesize that the assumption-free Bayesian approach (AFBA) can reduce sampling requirements, while improving the accuracy of results. Retrospective analysis of previously published CY PK data from 20 patients undergoing stem cell transplantation. In that study, Bayesian estimation based on the MAP approach of individual PK parameters was accomplished to predict individualized day-2 doses of CY. Based on these data, we used the AFBA to select the optimal sampling schedule and compare the projected probability of achieving the therapeutic end points. By optimizing the sampling schedule with the AFBA, an effective individualized PK characterization can be obtained with only two blood draws at 4 and 16 hours after administration on day 1. The second-day doses selected with the AFBA were significantly different than the MAP approach and averaged 37% higher probability of attaining the therapeutic targets. The AFBA, based on cutting-edge statistical and mathematical tools, allows an accurate individualized dosing of CY, with simplified PK sampling. This highly accessible approach holds great promise for improving efficacy, reducing toxicities, and lowering treatment costs.

Impact of Severe Hypothyroidism on Cyclophosphamide Disposition and Routes of Metabolism and Transport in a Patient with Treatment-Resistant Lupus Nephritis

To report what we believe to be the first case of severe hypothyroidism with reduced drug metabolism and transport activity. A 32-year-old African American woman with a history of treatment-resistant lupus nephritis and concurrent hypothyroidism was participating in a clinical study to evaluate cyclophosphamide pharmacokinetics in patients with glomerulonephritis due to lupus nephritis and small-vessel vasculitis. Thyroid-stimulating hormone levels ranged from 60 to 300 μIU/mL, despite high doses of thyroid replacement hormone (levothyroxine 400 μg twice weekly). The pharmacokinetics of the probe drug cocktail (flurbiprofen/fexofenadine) were altered, with formation clearance of flurbiprofen (CYP2C9 function) lower in our patient versus the average value in our study cohort, suggesting a reduction in activity. The area under the concentration-time curve from 0 to 24 hours for fexofenadine (transporter function) was 2-fold higher in our patient compared to that of other study patients. Pharmacokinetic data showed markedly decreased cyclophosphamide clearance and exposure to 4-hydroxycyclophosphamide, as well as a reduced metabolic ratio of 4-hydroxycyclophosphamide to cyclophosphamide. Previous cases of altered pharmacokinetics and toxicity of medications in patients with mild to moderate thyroid dysfunction have been published. Our case evaluated the impact of a severe form of hypothyroidism on cyclophosphamide pharmacokinetics and probe drug metabolism and transport. If changes were not demonstrated at the extreme spectrum of hypothyroidism, there would be little concern for changes in patients with less severe disease. Profound hypothyroidism likely contributed to the patient's poor response to cyclophosphamide treatment through its influence on CYP isoenzymes responsible for the activation to 4-hydroxycyclophosphamide and possibly through reduced transport function. Clinicians should monitor for significant hypothyroidism in patients who are prescribed drugs (eg, cyclophosphamide) that require metabolic conversion to form active therapeutic moieties.

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.

Cyclophosphamide followed by Intravenous Targeted Busulfan for Allogeneic Hematopoietic Cell Transplantation: Pharmacokinetics and Clinical Outcomes

Targeted busulfan (TBU) and cyclophosphamide (CY) for allogeneic hematopoietic cell transplantation carries a high risk of sinusoidal obstruction syndrome (SOS) in patients undergoing transplantation for myelofibrosis. We tested the hypothesis that reversing the sequence of administration (from TBU/CY to CY/TBU) would reduce SOS and day +100 nonrelapse mortality. We enrolled 51 patients with myelofibrosis (n = 20), acute myelogenous leukemia (n = 20), or myelodysplastic syndrome (n = 11) in a prospective trial of CY/TBU conditioning for allogeneic hematopoietic cell transplantation. CY 60 mg/kg/day i.v. for 2 days was followed by daily i.v. BU for 4 days, targeted to a concentration at steady state (Css) of 800-900 ng/mL. Compared with TBU/CY-conditioned patients, CY/TBU-conditioned patients had greater exposure to CY (P < .0001) and less exposure to 4-hydroxycyclophosphamide (P < .0001). Clinical outcomes were compared between cases and controls (n = 271) conditioned with TBU/CY for the same indications. In patients with myelofibrosis, CY/TBU conditioning was associated with a significantly reduced incidence of SOS (0% versus 30% after TBU/CY; P = .006), whereas the incidence of SOS was low in both cohorts with acute myelogenous leukemia/myelodysplastic syndrome. Day +100 mortality was significantly lower in the CY/TBU cohort (2% versus 13%; P = .01). CY/TBU conditioning had a marked affect on the pharmacokinetics of CY and was associated with significantly lower incidence of SOS and day +100 mortality, suggesting that CY/TBU is superior to TBU/CY as conditioning for patients with myelofibrosis.

Cyclophosphamide and 4‐hydroxycyclophosphamide pharmacokinetics in patients with glomerulonephritis secondary to lupus and small vessel vasculitis

Cyclophosphamide, the precursor to the active 4-hydroxycyclophosphamide, is used in active glomerulonephritis despite limited pharmacokinetics data. The pharmacokinetics of cyclophosphamide and 4-hydroxycyclophosphamide were evaluated. The influence of laboratory and pharmacogenomic covariates on pharmacokinetics was evaluated as a secondary aim. Glomerulonephritis patients (n = 23) participated in a pharmacokinetic evaluation. Blood was serially collected and assayed for cyclophosphamide and 4-hydroxycyclophosphamide by LC/MS methods. Kidney function, serum albumin and polymorphisms in drug metabolism or transport genes were evaluated. Analyses included non-compartmental pharmacokinetics and parametric and non-parametric statistics. The mean area under the plasma concentration-time curve (AUC(0,∞)) data were 110,100 ± 42,900 ng ml(-1) h and 5388 ± 2841 ng ml(-1) h for cyclophosphamide and 4-hydroxycyclophosphamide, respectively. The mean metabolic ratio was 0.06 ± 0.04. A statistically significant relationship was found between increased serum albumin and increased half-life (0.584, P = 0.007, 95% CI 0.176, 0.820) and a borderline relationship with AUC(0,∞) (0.402, P = 0.079, 95% CI -0.064, 0.724) for 4-hydroxycyclophosphamide. Covariate relationships that trended toward significance for cyclophosphamide included decreased serum albumin and increased elimination rate constant (-0.427, P = 0.061, 95% CI 0.738, 0.034), increased urinary protein excretion and increased AUC(0,∞) (-0.392, P = 0.064, 95% CI -0.699 to 0.037), decreased C(max) (0.367, P = 0.085, 95% CI -0.067, 0.684) and decreased plasma clearance (-0.392, P = 0.064, 95% CI -0.699, 0.037). CYP2B6*9 variants vs. wildtype were found to have decreased elimination rate constant (P = 0.0005, 95% CI 0.033, 0.103), increased V(d) (P = 0.0271, 95% CI -57.5, -4.2) and decreased C(max) (P = 0.0176, 95% CI 0.696, 6179) for cyclophosphamide. ABCB1 C3435T variants had a borderline decrease in cyclophosphamide elimination rate constant (P = 0.0858; 95% CI -0.005, 0.102). Pharmacokinetics of cyclophosphamide and 4-hydroxycyclophosphamide in patients with lupus nephritis and small vessel vasculitis are similar. Clinical and pharmacogenetic covariates alter disposition of cyclophosphamide and 4-hydroxycyclophosphamide. Clinical findings of worsened glomerulonephritis lead to increased exposure to cyclophosphamide vs. the active 4-hydroxycyclophosphamide, which could have relevance in terms of clinical efficacy. The CYP2B6*9 and ABCB1 C3435T polymorphisms alter the pharmacokinetics of cyclophosphamide and 4-hydroxycyclophosphamide in glomerulonephritis.

Aprepitant Pharmacokinetics and Assessing the Impact of Aprepitant on Cyclophosphamide Metabolism in Cancer Patients Undergoing Hematopoietic Stem Cell Transplantation

Aprepitant, a neurokinin antagonist, is an effective antiemetic agent in chemotherapy for delayed nausea and vomiting. The study objective was to evaluate the pharmacokinetics of aprepitant and concurrent cyclophosphamide (CY), often a component of hematopoietic stem cell transplant (HSCT) conditioning regimen, in cancer patients undergoing HSCT. Forty subjects were randomized to either aprepitant or placebo in addition to standard antiemetics. Aprepitant or placebo was started 1 hour before the first chemotherapy or radiation dose for HSCT conditioning and administered daily until 4 days after infusion of the hematopoietic cell graft (for a total of 10-12 days). Serial blood samples were collected for aprepitant and CY plus 2 important CY metabolites. The results indicate that aprepitant is well absorbed and does not auto-induce its metabolism. No significant drug interaction was observed with CY or its metabolites. A significant portion of the patients had subtherapeutic aprepitant concentrations; however, chemotherapy-induced nausea and vomiting were effectively managed. No dosage adjustment was necessary, and administration of aprepitant in HSCT at the prescribed dosage of 125 mg orally on day 1 and 80 mg orally on each consecutive day through day +4 after HSCT was well tolerated with no significant changes in CY pharmacokinetic parameters.

The effect of aprepitant and race on the pharmacokinetics of cyclophosphamide in breast cancer patients

The prodrug cyclophosphamide is metabolized by cytochrome P450(CYP)2B6 to the active metabolite, 4-hydroxycyclophosphamide (4-OH), and by CYP3A4/5 to toxic chloracetaldehyde and 2-dechloroethylcyclophosphamide (DCE). Since aprepitant is a moderate inhibitor of CYP3A4, the study was designed to determine whether its concurrent use alters the pharmacokinetics (PK) of cyclophosphamide. In addition, we sought to determine the effect of race and pharmacogenomics on cyclophosphamide PK. Eighteen patients with localized breast cancer were randomized in this double-blinded cross-over study to receive aprepitant or placebo in addition to cyclophosphamide 600 mg/m(2) and doxorubicin 60 mg/m(2). Blood samples were collected for both PK analysis of cyclophosphamide and metabolites and pharmacogenomic analysis. Single nucleotide polymorphisms genotyped were CYP3A4*1B, CYP3A5*3, and CYP2B6*6. The geometric mean area under concentration-time curve (AUC(0-t) μg/mL h) for cyclophosphamide was 282 following aprepitant and 230 following placebo (ratio 1.23; 90% CI 1.13, 1.33). 4-OH AUC(0-t) (μg/mL h) was 6.80 following aprepitant and 6.96 following placebo (ratio 0.98; 90% CI 0.88, 1.08). DCE AUC(0-t) (μg/mL h) was 6.76 following aprepitant and 9.37 following placebo (ratio 0.72; 90% CI 0.64, 0.81). Genotype analysis was confounded by race. Race was a significant predictor of DCE lnAUC(0-t) (P = 0.0169) as African Americans had approximately a 2-fold higher DCE AUC than Caucasians. Aprepitant altered the exposure of cyclophosphamide and DCE but not the active 4-OH metabolite, making it unlikely that aprepitant would change the clinical efficacy of cyclophosphamide. African Americans were also found to have altered PK compared with Caucasian patients.

Population pharmacokinetics of cyclophosphamide in patients with thalassemia major undergoing HSCT

CY in combination with BU is a widely used conditioning regimen for haematopoietic SCT (HSCT). The aim of this study was to evaluate the pharmacokinetics (PK) of CY and its major metabolite 4-hydroxyCY (HCY) in patients with thalassemia undergoing HSCT. A total of 55 patients received BU (16 mg/kg) followed by CY (160-200 mg/kg) both over 4 days before HSCT. A population PK model was developed to describe the disposition of CY and HCY and the inter-individual (IIV) and inter-occasion variability (IOV). The model was also used to determine the effects covariates including: demographics, Lucarelli classification and polymorphisms in enzymes involved in the metabolism or biotransformation of CY had on CY and HCY disposition. Overall, 17-114% IIV and 12-103% IOV in CY and HCY PK parameters were observed. Body weight and age were the main covariates, which explained the largest portion of the IIV. In addition, CYP2C9*2 explained a significant portion of the IIV in the clearance (P<0.002) and thus the area under the concentration curve (P<0.05) of CY. This covariate model may be used to design and plan targeted dose therapy in this group of pediatric patients, if clinical outcome association with CY PK are proved and target range established.

Pharmacokinetics of Cyclophosphamide after Oral and Intravenous Administration to Dogs with Lymphoma

Cyclophosphamide is an alkylating chemotherapeutic drug administered i.v. or p.o.. It is currently assumed that exposure to the active metabolite, 4-hydroxycyclophosphamide (4-OHCP), is the same with either route of administration. To characterize the pharmacokinetics of cyclophosphamide and 4-OHCP in dogs with lymphoma when administered p.o. or i.v.. Sixteen client-owned dogs with substage A lymphoma were enrolled in the study. Eight dogs received cyclophosphamide i.v. and 8 received it p.o.. Prospective randomized clinical trial was performed. Blood was collected from each dog at specific time points after administration of cyclophosphamide. The serum was evaluated for the concentration of cyclophosphamide and 4-OHCP with mass spectrometry and liquid chromatography. Drug exposure to cyclophosphamide measured by area under the curve (AUC)(0-inf) is significantly higher after intravenous administration (7.14 ± 3.77 μg/h/mL) compared with exposure after oral administration (P-value < .05). No difference in drug exposure to 4-OHCP was detected after i.v. (1.66 ± 0.36 μg/h/mL) or p.o. (1.42 ± 0.64 μg/h/mL) administered cyclophosphamide. Drug exposure to the active metabolite 4-OHCP is equivalent after administration of cyclophosphamide either p.o. or i.v..

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.

Pharmacokinetics of cyclophosphamide enantiomers in patients with breast cancer

Adjuvant chemotherapy with cyclophosphamide (CYC) is used for the treatment of breast cancer. CYC is used as a racemic mixture, although preclinical data have demonstrated differences in the efficacy and toxicity of its enantiomers, with (S)-(-)-CYC exhibiting a higher therapeutic index. The present study investigated the enantioselectivity and influence of CYP2B6, CYP2C9, CYP2C19, and CYP3A on the kinetic disposition of CYC in patients with breast cancer. Fifteen patients previously submitted to removal of the tumor and treated with racemic CYC (900 or 1,000mg/m(2)) and epirubicin were included in the study. The in vivo activity of CYP3A was evaluated using midazolam as a marker drug. Serial blood samples were collected up to 24h after administration of the first cycle of CYC. The kinetic disposition of CYC was enantioselective in patients with breast cancer, with plasma accumulation of the (S)-(-)-CYC enantiomer (AUC 195.0 vs. 174.8μgh/mL) due to the preferential clearance of the (R)-(+)CYC enantiomer (5.1 vs. 5.7 L/h). Clearance of either CYC enantiomer did not differ between the CYP2B6, CYP2C9, and CYP2C19 genotypes or as a function of the in vivo activity of CYP3A evaluated by midazolam clearance. The pharmacokinetics of CYC is enantioselective in patients with breast cancer concomitantly treated with epirubicin and ondansetron. Genotyping or phenotyping did not contribute to adjustment of the CYC dose regimen in patients included in this study.

Gene polymorphisms in cyclophosphamide metabolism pathway,treatment-related toxicity, and disease-free survival in SWOG 8897 clinical trial for breast cancer.

There are no established genetic markers for prediction of outcomes after cyclophosphamide (CP)-containing adjuvant therapy for breast cancer. In an ancillary study to a SWOG (Southwest Oncology Group) trial (S8897), we investigated functional polymorphisms in 4 genes in CP pharmacokinetic pathways in relation to hematologic toxicity and disease-free survival (DFS). Germline DNA was available from 458 women who were at high risk of relapse and was randomized to CAF (CP, intravenous doxorubicin, and 5-fluorouracil) versus CMF (CP, intravenous methotrexate, and 5-fluorouracil) ± tamoxifen, and from 874 women who had a presumed favorable prognosis and did not receive adjuvant therapy. Odds ratios for grade 3 and 4 hematologic toxicity in the treated group and hazard ratios for DFS associated with selected functional polymorphisms in CYP2B6CYP3A4GSTA1 and GSTP1 were estimated by logistic regression and Cox proportional hazard regression. Compared with women with AA genotypes, those with at least 1 GSTP1 variant G allele had reduced risk of grade 3 and 4 neutropenia [odds ratios (OR) = 0.63, 95% CI = 0.41-0.97] and leucopenia (OR = 0.59, 95% CI = 0.39-0.89). No other associations between single nucleotide polymorphisms and toxicity or survival were found in the treated or untreated group. Known genetic variants in genes involved in CP pharmacokinetics may not have major effects on DFS in breast cancer patients. The lower risk of developing high-grade hematologic toxicity among women with variant GSTP1 alleles suggests that genetic markers in combination with clinical factors may be useful in defining a subgroup of women who are less susceptible to adverse hematologic toxicities with CP-containing therapies.

Abstract 2758: Population pharmacokinetics of cyclophosphamide in infants and young children

Abstract Cyclophosphamide (CTX) is an anticancer pro-drug used for induction therapy of brain tumors and other malignancies. An adequate pharmacokinetic study of CTX and its active metabolite, 4-hydroxy-cyclophosphamide (4OH-CTX), has never been performed in infants and young children. We are therefore examining the disposition of CTX, 4OH-CTX, and its inactivated metabolite, carboxyethylphosphoramide mustard (CEPM), in children &amp;lt; 3 years of age with brain tumors. CTX was administered during the first course of treatment (1.5 g/m2 infused over 1 h), and serial samples were collected prior to infusion, at the end of infusion, and 3, 6, and 24 h after the end of infusion. CTX and CEPM were quantitated in plasma with a validated LC-MS/MS method and 4OH-CTX was stabilized by addition of phenylhydrazine to whole blood and quantitated with a validated LC-MS/MS method. A nonlinear mixed-effects model was fit to the data using NONMEM software and covariates were added to the model based on reduction in objective function value and improvement in diagnostic plots. Pharmacokinetic studies were performed with 28 patients. The median (range) age was 17.3 months (0.87 − 35.9 months) and median (range) BSA was 0.49 m2 (0.24 − 0.71 m2). A model with one compartment for CTX and each of its metabolites adequately described the data. BSA normalization of the dose reduced the inter-individual variability (IIV) in the volume of distribution of CTX (VCTX) from 32% to 13% and reduced the IIV in the elimination of 4OH-CTX through non-CEPM pathways (k4OH-CTX) from 60% to 38%. The covariate analysis showed that the BSA-normalized clearance of CTX to 4OH-CTX (CLCTX) increased slightly with age, whereas k4OH-CTX increased rapidly with age. The net effect was that exposure to 4OH-CTX decreased with age in a nonlinear fashion. These results demonstrate the importance of studying the pharmacokinetics of anticancer drugs in infants and young children, and will provide the basis for the rational design of CTX dosing strategies for infants and young children with brain tumors. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 2758.

Population pharmacokinetics of cyclophosphamide in patients with thalassaemia major undergoing HSCT shows body weight, CYP450, GST and ALDH polymorphisms as covariates explaining inter-individual variation

Abstract Abstract 1182 Poster Board I-204 Cyclophosphamide (Cy) in combination with busulfan is an important component of myeloablative conditioning regimen used prior to hematopoietic stem cell transplantation (HSCT) for both malignant and non-malignant conditions. We have previously reported up to 20 fold inter-individual variation in the pharmacokinetics (PK) of Cy in patients with beta thalassaemia undergoing HSCT [Blood (ASH Annual Meeting Abstracts), Nov 2004; 104: 99]. PK parameters of Cy have been shown to be associated with regimen related toxicity and outcome of transplant. To explain the basis of the inter-individual variation in Cy PK, we have developed a population PK model. We analyzed the PK of Cy in consecutive children with beta thalassaemia major who received HSCT from HLA identical matched sibling donor at the Christian Medical College, Vellore from 2001 till 2004. A total of 900 cyclophosphamide concentration measurements from 55 patients were included and correlated with age, sex, body weight and 10 polymorphisms in enzymes involved in the metabolism or biotransformation of Cy namely GST A1, M1, T1, P1, CYP2B6, CYP2C9, CYP2C19 and ALDH genes. Non-linear mixed effects modeling analysis was performed with Monolix (version 2.4, www.monolix.org ) to investigate the effect of patient covariates on PK, and to estimate the relative magnitude of inter-individual and inter-occasion variability. A two-compartment pharmacokinetic model was used to describe the data. The pharmacokinetic parameters estimated included elimination rate constant and volume (ke (1/hr), V (L or L/kg)), and the inter-compartmental parameters (k12 and k21 (1/hr)). The distribution of the parameters was assumed log-normal. Body weight was the main covariate which explained the largest portion of the IIV (28% and 20% of V and ke IIV, respectively). In addition, the following genotypes showed differences in the pharmacokinetics: GSTP1*B (1.7X higher ke in MUT versus WT or HET; p Disclosures: No relevant conflicts of interest to declare.