Pharmacokinetics Of Cyclophosphamide Research Articles

Association of cyclophosphamide pharmacokinetics to polymorphic cytochrome P450 2C19

Cyclophosphamide (CP), a widely used cytostatic, is metabolized by polymorphic drug metabolizing enzymes particularly cytochrome P450 (CYP) enzymes. Its side effects and clinical efficacy exhibit a broad interindividual variability, which might be due to differences in pharmacokinetics. CP-kinetics were determined in 60 patients using a global and a population pharmacokinetic model considering functionally relevant polymorphisms of CYP2B6, CYP2C9, CYP2C19, CYP3A5, and GSTA1. Moreover, metabolic ratios were calculated for selected CP metabolites, analyzed by (31)P-NMR-spectroscopy. Analysis of variance revealed that the CYP2C19*2 genotype influenced significantly pharmacokinetics of CP at doses </=1000 mg/m(2), whereas there was no evidence of an association of other genotypes to CP elimination or clearance. Mean (+/-SD) CP elimination constants k(e) (h(-1)) were 0.109+/-0.025 in 44 CYP2C19*1/*1 subjects, 0.088+/-0.018 in 13 CYP2C19*1/*2, and 0.076+/-0.014 in three inactive CYP2C19*2/*2 carriers (P=0.009). At CP doses higher than 1000 mg/m(2), a significantly increase of elimination was observed (P=0.001), possibly due to CYP induction. Further studies should link these findings with the clinical outcome.

The effect of ciprofloxacin on cyclophosphamide pharmacokinetics in patients with non‐Hodgkin lymphoma

Cyclophosphamide (CPA) is widely used in chemotherapy. The CPA is a prodrug that requires metabolic transformation to generate the active metabolite, 4-hydroxy-CPA (4-OH-CPA). Ciprofloxacin (CF) is a fluoroquinolone antibiotic with a broad spectrum that is commonly used in treatment of a variety of infections. It has been reported that prophylactic administration of CF during CPA conditioning was a high-risk factor for relapse in patients undergoing allogeneic bone marrow transplantation. In the present study we investigated the pharmacokinetics of CPA and 4-OH-CPA in eight non-Hodgkin lymphoma (NHL) patients treated with CPA together with or without CF. Clearance and distribution volumes of CPA were significantly (P < 0.01) lower (4.7 L/h and 42.3 L, respectively) when patients were treated with CF prior to CPA compared to that observed when the patients did not receive CF (5.9 L/h and 48.1 L, respectively). No change in the elimination half-life was observed. The CF administration prior to CPA has resulted in significantly (P < 0.01) lower exposure to 4-OH-CPA as expressed as area under the plasma concentration curve (AUC). The metabolic ratio AUC(4-OH-CPA)/AUC(CPA) was lower in all patients treated with CF prior to CPA compared to that observed when patients received CPA only (P = 0.008). Our study showed that CF administration alters CPA kinetics in patients with NHL. Other antibiotics than these contain fluoroquinolones should be used during CPA therapy.

Aprepitant inhibits cyclophosphamide bioactivation and thiotepa metabolism

Patients receiving the highly emetogenic high-dose chemotherapy regimen with cyclophosphamide, thiotepa and carboplatin (CTC) may benefit from the neurokin-1 receptor antagonist aprepitant in addition to standard anti-emetic therapy. As aprepitant has been shown to be a moderate inhibitor of the cytochrome P450 (CYP) 3A4 isoenzyme, its effect on the pharmacokinetics and metabolism of cyclophosphamide and thiotepa was evaluated. Moreover, preliminary results on the clinical efficacy of aprepitant in the CTC regimen are reported. Six patients were enrolled in a protocol that employed a 4-day course of CTC high-dose chemotherapy with cyclophosphamide (1,500 mg/m2/day), thiotepa (120 mg/m2/day) and carboplatin (AUC 5 mg min/ml/day). Two patients received the tCTC protocol, which comprises two-third of the dose of CTC. In addition to standard anti-emetic therapy, the patients received aprepitant from one day before the start of their course until 3 days after chemotherapy. Blood samples were collected on days one and three of the course and analyzed for cyclophosphamide and its activated metabolite 4-hydroxycyclophosphamide, thiotepa and its main active metabolite tepa. The influence of aprepitant on the pharmacokinetics of cyclophosphamide and thiotepa was analyzed using a population pharmacokinetic analysis including a reference population of 49 patients receiving the same chemotherapy regimen without aprepitant and sampled under the same conditions. The frequency of nausea and vomiting in the six patients receiving CTC was compared with those of the last 22 consecutive patients receiving CTC chemotherapy without aprepitant. Inhibitory activity of aprepitant on cyclophosphamide and thiotepa metabolism was also tested in human liver microsomes. In our patient population, the rate of autoinduction of cyclophosphamide (P=0.040) and the formation clearance of tepa (P<0.001) were reduced with 23% and 33% when aprepitant was co-administered, respectively. Exposures to the active metabolite 4-hydroxycyclophosphamide and tepa were therefore reduced (5% and 20%, respectively) in the presence of aprepitant. In human liver microsomes, the 50% inhibitory concentrations (IC50) of aprepitant for inhibition of cyclophosphamide (IC50=1.3 microg/ml) and thiotepa (IC50=0.27 microg/ml) metabolism were within the therapeutic range. Patients receiving aprepitant experienced less frequently CINV both during and after the CTC course compared with the reference population (nausea 3.7 days vs. 5.8 days, P=0.052; vomiting 0.5 days vs. 4.8 days, P<0.001). Aprepitant inhibited both cyclophosphamide and thiotepa metabolism, most probably due to inhibition of the CYP 3A4 and/or 2B6 isoenzymes. The effects of this interaction are, however, small compared to the total variability. Addition of aprepitant may provide superior protection against vomiting in patients receiving the highly emetogenic high-dose CTC chemotherapy.

Clinical Pharmacokinetics of Cyclophosphamide

Cyclophosphamide is an extensively used anticancer and immunosuppressive agent. It is a prodrug undergoing a complicated process of metabolic activation and inactivation. Technical difficulties in the accurate determination of the cyclophosphamide metabolites have long hampered the assessment of the clinical pharmacology of this drug. As these techniques are becoming increasingly available, adequate description of the pharmacokinetics of cyclophosphamide and its metabolites has become possible. There is incomplete understanding on the role of cyclophosphamide metabolites in the efficacy and toxicity of cyclophosphamide therapy. However, relationships between toxicity (cardiotoxicity, veno-occlusive disease) and exposure to cyclophosphamide and its metabolites have been established. Variations in the balance between metabolic activation and inactivation of cyclophosphamide owing to autoinduction, dose escalation, drug-drug interactions and individual differences have been reported, suggesting possibilities for optimisation of cyclophosphamide therapy. Knowledge of the pharmacokinetics of cyclophosphamide, and possibly monitoring the pharmacokinetics of cyclophosphamide in individuals, may be useful for improving its therapeutic index.

Cyclophosphamide disposition in an anephric child

Although limited data are available about cyclophosphamide disposition in patients with renal insufficiency, nothing has been reported in anephric patients. We characterized cyclophosphamide pharmacokinetics in an anephric child with bilateral Wilms tumor, both on (day 1) and off (day 2) hemodialysis. The median cyclophosphamide clearance on and off hemodialysis was 5.34 and 3.82 L/hr*m(2), respectively, demonstrating elimination of cyclophosphamide in this anephric child. The off hemodialysis clearance was similar to that in children with normal renal function. Hydroxycyclophosphamide (HCY) AUC was 20.6 and 8.77 microM*hr on and off hemodialysis. Carboxyethylphosphoramide mustard (CEPM) AUC obtained on hemodialysis (i.e., 194 microM*hr) was similar to that in children with normal renal function, although an elevated CEPM AUC was observed when hemodialysis was not received (i.e., 383 microM*hr). With the recent findings that clinical outcomes are related to CEPM AUC, further data are needed regarding the pharmacokinetics of cyclophosphamide and relevant metabolites in anephric children.

Quantitative Pharmacogenetics of Cyclophosphamide in Patients with Hematological Malignancies.

A high degree of interindividual variation in cyclophosphamide (CPA) pharmacokinetics was reported in certain cancer patient groups. To better understand the mechanisms underlying the variation in CPA metabolism, the pharmacokinetics of CPA and its active metabolite 4-OH-CPA were estimated in patients with hematological tumors and related to the genotype of CYP2B6, CYP2C9 and CYP2C19. The influence of liver function on CPA metabolism was also evaluated.Twenty-nine patients with hematological malignancies (MM, ALL or NHL) treated with a conventional CPA dose (1 g/m²) were recruited to this study. Blood samples were collected before, during and after CPA treatment. HPLC was used to measure plasma concentrations of CPA and 4-OH-CPA. Patients were genotyped for the CYP2B6 G516T, CYP2C9*2, CYP2C9*3, CYP2C19*2 and CYP2C19*3 alleles. Serum bilirubin levels were measured before the treatment. Data was analyzed individually and by population pharmacokinetic methods, using non-linear mixed effect modeling. The interindividual variability in exposure to CPA, 4-OHCPA and 4-OH-CPA/CPA was 5.8-, 3.3- and 10.3- fold, respectively. A positive correlation was found between half-lives of CPA and 4-OH-CPA (p<0.05) and there was a significant negative correlation between AUCs of CPA and 4-OH-CPA. In the population analysis the clearance contribution of the CYP2B6 G516T variant allele was about twice the wild type gene while the genotype of CYP2C9 did not influence clearance. A negative correlation was observed between bilirubin level and CPA bioactivation. There is a considerable variation in CPA formation of 4-OH-CPA among patients. The liver function influences CPA metabolism. Presence of the CYP2B6 G516T mutation increases the rate of 4-OH-CPA formation, a substantial variation among patients remain to be explained.

High Dose Celecoxib and Metronomic ‘Low-Dose' Cyclophosphamide Is Effective Therapy in Patients with Relapsed and Refractory Aggressive Histology NHL.

Background: Relapsed aggressive histology non-Hodgkin's lymphoma (NHL) has a poor prognosis, and new treatments are needed. Angiogenesis is increased in aggressive NHL and may be a target in these diseases. Low-dose chronic chemotherapy (metronomic chemotherapy, MC) inhibits angiogenesis in vitro and in vivo. Since COX-2 may promote neoplasia and tumor angiogenesis, selective COX-2 inhibitors may have antitumor effects in NHL. We assessed response and toxicity to MC and COX-2 inhibition in patients (pts.) with relapsed aggressive NHL following anthracycline-based chemotherapy.Methods: Pts. with measurable disease and normal renal function received cyclophosphamide 50 mg po qd + celecoxib 400 mg po bid. Pts. were assessed clinically and radiologically in serial fashion. We measured serial plasma VEGF and TSP-1 levels and pharmacokinetics (PK) were performed in selected pts. Serial circulating endothelial cells (CEC) and their precursors (CEP) were measured by flow cytometry as of October 2003.Results: To date, 29 of a planned 32 pts. have been enrolled; 3 are ineligible and 25 are evaluable for response. Median age: 62 y (range 22–83). Histology: 17 DLBCL, 1 MCL, 3 transformed (CLL+FL), 2 T cell, 3 anaplastic large cell. Median 2.7 yrs from diagnosis (range 0.5–9.5); Median # of previous chemotherapy regimens: 3 (range 1–6); 31% were chemoresistant to preceding regimen; 8 had undergone prior ASCT. Median time to death or last follow-up: 4 mos (range 0.9–22).Response:10/25 pts. responded (2 CR/CRu, 8 PR, ORR 40%) at a median time of 4.6 mos, and at last f/up, 6/10 remained in PR at 22, 21, 16, 11, 8 and 7 mos. respectively. Three pts. achieved stable disease (SD) but 2 later progressed at a median time of 6 mos (range 4–14 mos) and 12/25 progressed primarily (PD) at a median time of 1.9 mos (range <1–9); 10 have died of NHL (median time 4 mos). 2 partial responders discontinued treatment in PR at 21 and 16 mos for cumulative cyclophosphamide exposure exceeding 40,000 mg. Both progressed within 2–3 months of drug disontinuation. Median OS and PFS are 8.5 and 3.9 mos, respectively.Adverse events (# pts): grade 3–4 ANC (2), grade 3 plt (3), grade 3 hypertension (1), grade 3 atrial arrhythmia(1) and grade 3 drug rash (1). Plasma VEGF and TSP-1 levels do not appear to correlate with response but the number of circulating endothelial cells (CEC) and their precursors (CEP) decline in responders. Celecoxib and cyclophosphamide pharmacokinetics will be presented. This regimen has been well tolerated with minimal GI toxicity. 90% of responders had normal LDH compared with 25% with PD. No patient with preceding chemoresistance responded.Conclusions: MC with high-dose celecoxib and low-dose cyclophosphamide is well tolerated and active in 40% of heavily pre-treated patients with relapsed aggressive NHL. The anti-angiogenic activity of this regimen is still being determined.

Diminishing the risk of nonrelapse mortality in hematopoietic stem cell transplantation: Prediction of exposure to the cyclophosphamide metabolite carboxyethylphosphoramide mustard.

Our objectives were (1) to develop a population pharmacokinetic model for cyclophosphamide, 4-hydroxycyclophosphamide, and carboxyethylphosphoramide mustard (a reporter for nonrelapse mortality) in hematopoietic stem cell transplantation patients and (2) to validate a Bayesian approach to dosing. In this study 147 patients received intravenous infusions of 60 mg. kg -1. d -1 cyclophosphamide for 2 days, followed by 12 to 14.4 Gy total body irradiation. A population model was developed to fit concentration-time data of cyclophosphamide and metabolites. Bayesian prediction of the area under the curve (AUC) was validated by dividing the data set into an index set (98 patients) and validation set (49 patients). Parameters from the index data set were used as priors. Cyclophosphamide elimination was best described by noninducible and inducible routes producing 4-hydroxycyclophosphamide. Induction was described by a zero-order maximum fold of induction-type increase in enzyme level. The prediction of the AUC of carboxyethylphosphoramide mustard was clinically accurate and precise (mean prediction error = -3.5% and root mean squared prediction error = 12.2%) with data limited to 5 to 6 points obtained in the first 16 hours. However, the AUC of 4-hydroxycyclophosphamide was overestimated (mean prediction error = 16.9%-23.6%). Several alternative models did not improve the result. The integrated mechanism-based model describes the pharmacokinetics of cyclophosphamide and carboxyethylphosphoramide mustard. Accurate modeling of 4-hydroxycyclophosphamide is limited by its chemical instability. Exposure to carboxyethylphosphoramide mustard could be accurately and precisely predicted with minimal data obtained over a 16-hour period after the first dose, offering the potential of pharmacokinetically guided dosing to reduce the nonrelapse mortality rate.

Cyclophosphamide pharmacokinetics in paediatric NHL

Cyclophosphamide pharmacokinetics in paediatric NHL

Alteration of pharmacokinetics of cyclophosphamide and suppression of the cytochrome p450 genes by ciprofloxacin.

Recently, it has been reported that prophylactic administration of ciprofloxacin during cyclophosphamide (CY) conditioning was a high-risk factor for relapse in patients undergoing allogeneic BMT. In the present study, we investigated the possible mechanisms of this interaction in male Sprague-Dawley rats. The kinetics of CY and its active 4-OH-CY metabolite were determined, after 3 days pretreatment with ciprofloxacin (200 mg/kg) and compared to control rats without treatment. CY was administered as a high or low single intravenous dose (150 and 90 mg/kg, respectively). The expression of the CYP2B1, CYP2B2, CYP2C11, CYP3A1 and CYP3A2 genes was evaluated by SYBR Green I Dye real-time PCR for quantification of mRNA. The administration of ciprofloxacin resulted in a significant increase in the AUC (P=0.007) and a significant decrease in clearance (P=0.007) when CY was given as a high dose. In accordance, the metabolic ratio (AUC4-OH-CY/AUCCY) was significantly lower (P=0.007) compared to that found in the control group. Ciprofloxacin significantly suppressed gene expression of CYP2C11 (P=0.01) and CYP3A1 (P=0.04); however, no effect was observed on the gene expression of CYP3A2, CYP2B1 and CYP2B2. Our study revealed that ciprofloxacin interacts with CY and suppressed relevant cytochromes p450 at the transcriptional level. This study may have a great clinical impact when ciprofloxacin is used in therapy.

Cyclophosphamide pharmacokinetics and dose requirements in patients with renal insufficiency

Intravenous pulse administration of cyclophosphamide (CYC) has been successfully used for the treatment of various autoimmune diseases. These patients often present with impaired renal function or even end-stage renal failure. Nevertheless, data concerning pharmacokinetics of CYC in renal insufficiency (RI) and on hemodialysis (HD) are rare and contradictory. The pharmacokinetics of CYC (0.5 to 1 g/m2 as a one-hour infusion) were determined in patients with renal involvement of autoimmune diseases. Group A (N = 6) patients had a creatinine clearance (CCr) of 25 to 50 mL/min, group B patients' (N = 5) CCr was 10 to 24 mL/min, and group C (N = 6) patients had CCr values <10 mL/min and HD. Concentrations of CYC in serum, dialysate and urine were measured by HPLC. Twelve previously investigated patients with normal renal function served as controls. Mean clearance (CL) of CYC was significantly reduced with decreased renal function (79 vs. 57 and 47 mL/min, controls vs. A and B, respectively, P < 0.05), but only moderately lower in the patients who received a three-hour HD during the study period (group C, 64 mL/min, NS). This resulted in reciprocal increases in systemic drug exposure (dose corrected AUC was 216, 298, 382 and 266 microg x h/mL x g, controls, A, B and C, respectively). Urinary excretion of CYC was markedly reduced in all patients with RI (renal CL was 14.9 vs. 3.4, 2.4 and 2.1 mL/min, controls vs. A, B and C, respectively, P < 0.001). However, in patient group C, a mean of 22% of administered CYC dose was eliminated by a three hour HD starting seven hours after CYC administration. Individual CCr values were significantly (P < 0.001) correlated with renal and systemic CL of CYC, respectively, and negatively correlated with dose corrected AUC. Clearance of CYC is decreased in patients with reduced renal function, thereby resulting in an increased systemic drug exposure. However, in hemodialysis-dependent patients, removal of CYC into the dialysate has to be taken into account. For optimal dosing of CYC in patients with renal insufficiency, the severity of renal impairment and the use and timing of hemodialysis have to be considered.

Relationship between exposure and toxicity in high-dose chemotherapy with cyclophosphamide, thiotepa and carboplatin

BackgroundHigh-dose chemotherapy in combination with peripheral blood progenitor cell transplantation is widely used in the treatment of several malignancies. The use of high-dose chemotherapy can be complicated by the occurrence of severe and sometimes life threatening toxicity. A wide interpatient variability in toxicity is encountered, which may be caused by variability in the pharmacokinetics of the agents. The aim of this study was to establish the pharmacokinetics of cyclophosphamide, thiotepa, carboplatin and all relevant metabolites in a widely used high-dose combination and to study possible relationships between the pharmacokinetics and toxicity. Patients and methodsBlood samples were collected from patients treated with modifications of the CTCb regimen consisting of cyclophosphamide (1000–1500 mg/m2/day), carboplatin (265–400 mg/m2/day) and thiotepa (80–120 mg/m2/day) as short infusions for four consecutive days. Thiotepa and its main metabolite tepa, ultrafilterable carboplatin, cyclophosphamide and its activated metabolites 4-hydroxycyclophosphamide and phosphoramide mustard were determined. Pharmacokinetics were assessed with the use of population pharmacokinetic analyses. Relationship between the area under the concentration–time curves (AUCs) of these compounds and toxicity were tested. ResultsA total of 46 patients (83 courses of chemotherapy) was included. Relationships were iden-tified between elevation of transaminases and the thiotepa and tepa AUC, mucositis and the tepa AUC and ototoxicity and the carboplatin AUC. A strong trend between the 4-hydroxycyclophosphamide AUC and veno-occlusive disease was found. ConclusionsThe complex pharmacokinetics of the different agents and their metabolites have been established and several relationships between the pharmacokinetics and toxicity were identified. These findings may form the basis for further treatment optimisation and dose-individualisation in this high-dose chemotherapy combination.

Consolidation therapy for childhood acute lymphoblastic leukaemia: clinical and cellular pharmacology of cytosine arabinoside, epipodophyllotoxins and cyclophosphamide

The intensification of post-remission induction therapy has been shown to improve the relapse-free survival for childhood acute lymphoblastic leukaemia (ALL), and is now a standard component of the treatment of childhood acute lymphoblastic leukaemia. For cytosine arabinoside (ara-C), methotrexate, vincristine and corticosteroids, in-vitro studies indicate that the extracellular drug concentration and exposure time are important determinants of cytotoxicity for human leukaemia cell lines. For L-asparaginase, epipodopyllotoxins and cyclophosphamide, there have been few studies of the relationship between cellular pharmacology and cytotoxicity in relation to ALL. The clinical and cellular pharmacology of methotrexate and cytosine arabinoside have been studied in relation to childhood ALL in vivo. For these drugs, there is evidence to suggest that maintenance of plasma concentrations that are biochemically optimal is necessary to maximize anti-leukaemic effects. For cytosine arabinoside in particular, optimal extracellular fluid concentrations are not likely to be achieved or maintained by bolus or short-duration i.v. infusions. A potentially important example of this may be served by the success of antimetabolite-based intrathecal chemotherapy for CNS-directed treatment of childhood ALL. Intrathecal administration of both methotrexate and cytosine arabinoside results in prolonged leukaemic cell exposure to cytotoxic concentrations of the drug. For vincristine, anthracyclines and asparaginase, the actual dose intensity received by children during consolidation therapy may be important, and there is considerable interpatient variation in the pharmacokinetics of cyclophosphamide and teniposide in the therapy of childhood cancers. The importance of this relationship to childhood ALL is not known. The pharmacological and cellular pharmacological studies performed at St Jude Children's Research Hospital (Memphis, TN, USA) have allowed investigation of the relationships between the clinical and cellular pharmacology of methotrexate and prognosis, and have supported the individualization of consolidation therapy with this drug. Cytosine arabinoside has been less well studied in relation to childhood ALL, although evidence exists to suggest that the administration of conventional-dose bolus or infusion schedules may not be optimal in terms of the antileukaemic efficacy of this antimetabolite. For L-asparaginase, ongoing studies may allow the relationship between dose and schedule of administration to be related to pharmacodynamic measures such as asparagine depletion and prognosis. Therefore, through knowledge of clinical and cellular pharmacological properties, it may be possible to optimize the consolidation phase of therapy for childhood ALL, without disrupting the fundamental principles by which the overall treatment is administered. This may be particularly important for children with disease that has inherent or acquired resistance to therapy.

A mechanism-based pharmacokinetic model for the cytochrome P450 drug-drug interaction between cyclophosphamide and thioTEPA and the autoinduction of cyclophosphamide.

Cyclophosphamide (CP) is widely used in high-dose chemotherapy regimens in combination with thioTEPA. CP is a prodrug and is activated by cytochrome P450 to 4-hydroxycyclophosphamide (HCP) which yields the final cytotoxic metabolite phosphoramide mustard (PM). The metabolism of CP into HCP exhibits autoinduction but is inhibited by thioTEPA. The aim of this study was to develop a population pharmacokinetic model for the bioactivation route of CP incorporating the phenomena of both autoinduction and the drug-drug interaction between CP and thioTEPA. Plasma samples were collected from 34 patients who received high-dose CP, thioTEPA and carboplatin in short infusions during 4 consecutive days. Elimination of CP was described by a noninducible route and an inducible route leading to HCP. The latter route was mediated by a hypothetical amount of enzyme. Autoinduction leads to a zero-order increase in amount of this enzyme during treatment. Inhibition by thioTEPA was modeled as a reversible, competitive, concentration-dependent inhibition. PM pharmacokinetics were described by first-order formation from HCP and first-order elimination. The final models for CP, HCP, and PM provided an adequate fit of the experimental data. The volume of distribution, noninducible and initial inducible clearances of CP were 31.0 L, 1.58 L/hr and 4.76 L/hr, respectively. The enzyme amount increased with a zero-order rate constant of 0.041 amount * hr-1. After each thioTEPA infusion, however, approximately 80% of the enzyme was inhibited. This inhibition was reversible with a half-life of 6.5 hr. The formation and elimination rate constants of PM were 1.58 and 0.338 hr-1, respectively. The developed model enabled the assessment of the complex pharmacokinetics of CP in combination with thio TEPA. This model provided an adequate description of enzyme induction and inhibition and can be used for treatment optimization in this combination.

Reduction of cyclophosphamide bioactivation by thioTEPA: critical sequence-dependency in high-dose chemotherapy regimens

Cyclophosphamide and thioTEPA are frequently used simultaneously in high-dose chemotherapy regimens. During a pharmacokinetic study of 31 courses in 20 patients of cyclophosphamide and its activated metabolite 4-hydroxycyclophosphamide given in the combination cyclophosphamide thioTEPA carboplatin, a sharp decrease in 4-hydroxycyclophosphamide concentration was observed immediately after the start of the thioTEPA infusion. A drug-drug interaction was suspected. This putative interaction was investigated in this study. Possible sequence dependency, due to inhibition of the formation of 4-hydroxycyclophosphamide by thioTEPA, was investigated by altering the sequence of infusion in three patients (four courses) receiving high-dose chemotherapy with cyclophosphamide (1,000 or 1,500 mg/m2 per day), thioTEPA (80 or 120 mg/m2 per day) and carboplatin (265 or 400 mg/m2 per day) in short infusions for four consecutive days. The pharmacokinetics of cyclophosphamide and 4-hydroxycyclophosphamide were established. Possible inhibition of the metabolism of cyclophosphamide and thioTEPA was investigated in human microsomes. A striking sequence dependency of the pharmacokinetics of 4-hydroxycyclophosphamide was observed. Administration of thioTEPA 1 h prior to cyclophosphamide resulted in decreased Cmax (-62%) and AUC (-26%) values of 4-hydroxycyclophosphamide compared to those of thioTEPA administered 1 h after cyclophosphamide. In human microsomes an inhibition of the conversion of cyclophosphamide to 4-hydroxycyclophosphamide by thioTEPA was observed at clinically relevant concentrations with an IC50 of 23 microM. No inhibition of the formation of TEPA by cyclophosphamide was observed. ThioTEPA strongly inhibits the bioactivation of cyclophosphamide and this may decrease both efficacy and toxicity. Our results seriously question the practice of the simultaneous continuous infusion of cyclophosphamide and thioTEPA and suggest that the sequencing and scheduling of these two agents in high-dose chemotherapy regimens may be of critical importance.

Novobiocin in combination with high-dose chemotherapy for the treatment of advanced breast cancer: A phase 2 study

We conducted the first phase 2 and pharmacologic study to evaluate the combination of novobiocin (a coumeromycin antibiotic that has been shown to augment alkylating agent cytotoxicity in experimental models) and high-dose cyclophosphamide and thiotepa followed by autologous marrow support in women with chemosensitive advanced breast cancer. Its aims were (1) to determine progression-free survival (PFS) and overall survival (OS), (2) to evaluate the pharmacokinetics of cyclophosphamide and thiotepa, and (3) to measure the ability of novobiocin to reverse alkylator drug resistance in vitro. Forty-one women with chemotherapy-responsive advanced breast cancer received cyclophosphamide (4 g/m2) for peripheral blood stem cell mobilization (treatment 1) followed by high-dose cyclophosphamide (1.5 g/m2 per day for 4 days), thiotepa (200 mg/m2 per day for 4 days), and novobiocin (4 g/day orally for 7 days) (treatment 2) and autologous marrow support. The median PFS was 10 months (range, 0.2-70.6 months) and OS, 21.5 months (range, 0.2-70.6 months). There was no statistically significant relationship between PFS or OS and area-under-the-curve values of cyclophosphamide, thiotepa, or 4-hydroxycyclophosphamide. Patient plasma samples (n = 12) obtained during novobiocin therapy were able to reverse alkylator drug resistance in an in vitro colony-forming assay. Correlative laboratory studies in an in vitro model system demonstrated that patient plasma after novobiocin treatment resulted in the magnitude of resistance reversal that had been predicted by prior preclinical experiments. Clinically, however, this activity of novobiocin did not translate into a substantial increase in PFS or OS compared with historical controls treated with high-dose alkylator therapy alone. Biol Blood Marrow Transplant 2000;6(3A):335-43.

The influence of interferon‐α on the pharmacokinetics of cyclophosphamide and its 4‐hydroxy metabolite in patients with multiple myeloma

The pharmacokinetics of cyclophosphamide (CP) and its cytotoxic metabolite 4-hydroxycyclophosphamide (4-OHCP) have been studied in multiple myeloma patients treated with the CIB (CP, interferon-alpha (IFN-alpha) and betamethasone) regimen. In the present investigation we aimed to determine whether exposure to CP and its cytotoxic metabolite 4-OHCP is influenced by the concomitant administration of IFN-alpha. Ten patients with previously untreated multiple myeloma entered the study. Each patient received two courses of CIB in randomized order. Interferon was administered either 2 h before the CP infusion in one course or 24 h after the CP infusion in the other course. A cyclophosphamide dose of 750-900 mg/m2 was given as a 2 h constant infusion. Interferon-alpha (10-15 x 10(6) IE) was given subcutaneously. All patients received betamethasone 24 h after CP or later. The elimination of CP was described by monoexponential decay. The administration of IFN-alpha before CP caused a decrease in CP clearance to 63% (P=0.004), a 137% longer half-life (P = 0.004) and a 137% higher peak plasma concentration (P = 0.006) compared to the results obtained when IFN-alpha was administered 24 h after CP. The formation of 4-OHCP was also affected by the administration of IFN-alpha prior to CP, 45% less exposure to 4-OHCP expressed as AUC (P = 0.002) and a 61% lower peak plasma concentration (P = 0.002) compared with that observed when IFN-alpha was administered 24 h after CP. The administration of IFN-alpha after CP resulted in a greater (45%, P = 0.02) decrease in leukocyte count compared with results when IFN-alpha was given before CP. This study demonstrates that the administration of IFN-alpha prior to CP significantly impairs pharmacokinetics of CP and 4-OHCP. When IFN-alpha was administered after CP, a higher exposure to the cytotoxic metabolite 4-OHCP was observed and reflected by a significant decrease in leukocyte count compared to that when IFN-alpha was given before CP. In conclusion, the time of administration of IFN-alpha in relation to concomitant chemotherapy (CP) has to be considered to obtain a higher efficacy of IFN-alpha/alkylating agent combining regimens for induction in multiple myeloma and related disorders.

The influence of busulphan on the pharmacokinetics of cyclophosphamide and its 4-hydroxy metabolite: time interval effect on therapeutic efficacy and toxicity.

The influence of busulphan on the pharmacokinetics of cyclophosphamide and its 4-hydroxy metabolite: time interval effect on therapeutic efficacy and toxicity.

Possible Influence of Prednisone on the Pharmacokinetics of Cyclophosphamide in Systemic Vasculitis

Objective: To evaluate whether the pharmacokinetics of cyclophosphamide and its metabolite 4-hydroxycyclophosphamide/aldophosphamide (4-OH-CP/AP) changed between the first and sixth cycles in patients with systemic vasculitis receiving intravenous cyclophosphamide every 3 weeks with a daily dose of prednisone. Patients and Methods: Seven patients (five women and two men) with systemic vasculitis were included. Cyclophosphamide was administered at a dose of 0.6 g/m2 as a 1-hour intravenous infusion every 3 weeks for 6 cycles. All patients were concomitantly taking daily oral prednisone 1 mg/kg started at the same time as the cyclophosphamide administration. Serum cyclophosphamide and 4-OH-CP/AP concentrations were assayed by high pressure liquid chromatography. Results: The mean concentrations and pharmacokinetic parameters of cyclophosphamide [terminal elimination half-life (t1/2β) 5.2 ± 2.2h, total body clearance (CLtotal) 5.8 ± 1.3 L/h, volume of distribution during the terminal phase (Vβ) 0.8 ±0.39 L/kg) and 4-OH-CP/AP (t1/2β 6.4 ± 2.9h) at the first course were consistent with those observed in cancer patients. Comparison of pharmacokinetics between the first and the sixth cycles showed that they had changed by the sixth cycle, with a significantly smaller mean area under the curve of serum 4-OH-CP/AP concentration versus time (2.04 vs 0.94 mg/L·h, p = 0.043) and, in parallel, a significantly larger mean area under the curve of serum cyclophosphamide concentration versus time (174.5 vs 248.1 mg/L·h, p = 0.019). The mean CLtotal for cyclophosphamide was significantly lower at the sixth cycle (5.8 vs 4.0 L/h, p = 0.017). Conclusion: These findings in seven patients suggest a potential influence of prednisone on cyclophosphamide metabolism when the two agents are given concomitantly over the long term. Although the clinical significance of this interaction is unclear, 4-OH-CP/AP is probably responsible for the cytotoxic activity of cyclophosphamide and increasing the cyclophosphamide dose should be considered for subsequent cycles. This approach merits further investigation.

Pharmacokinetics of cyclophosphamide and its metabolites in bone marrow transplantation patients.

To characterize the pharmacokinetics of cyclophosphamide and 5 of its metabolites in bone marrow transplant patients and to identify the mechanism of the increase in 4-hydroxycyclophosphamide area under the plasma concentration-time curve (AUC) from day 1 to day 2 of cyclophosphamide administration. Cyclophosphamide was administered by intravenous infusion (60 mg/kg over 1 hour, once a day) for 2 consecutive days to 18 patients. Cyclophosphamide and 4-hydroxycyclophosphamide concentration time data on day 1 and day 2 were fitted to a model to estimate 4-hydroxycyclophosphamide formation (CLf) and elimination (CLm) clearances. Erythrocyte aldehyde dehydrogenase-1 activity was measured ex vivo just before the first cyclophosphamide infusion was started (0 hours) and 24 hours after the second cyclophosphamide infusion (48 hours). From day 1 to day 2, the AUC of cyclophosphamide, deschloroethyl cyclophosphamide and phosphoramide mustard decreased 24.8%, 51%, and 29.4% (P < .02), the AUC of 4-hydroxycyclophosphamide and carboxyethylphosphoramide mustard increased 54.7% and 25% (P < .01), whereas the AUC of phosphoramide mustard was not significantly changed (P > .3). The CLf of 4-hydroxycyclophosphamide increased 60% (P < .001), its CLm decreased 27.7% (P < .001), and the fraction of cyclophosphamide dose converted to 4-hydroxycyclophosphamide increased 16% (P < .001) from day 1 to day 2. The activity of patient erythrocyte aldehyde dehydrogenase-1 decreased 23.3% (P < .02) from 0 hours to 48 hours. The AUC of 4-hydroxycyclophosphamide increased from day 1 to day 2 as a result of increased formation and decreased elimination clearances of 4-hydroxycyclophosphamide. Aldehyde dehydrogenase-1 activity appears to decline as a consequence of cyclophosphamide administration.