Disposition of total and unbound etoposide following high-dose therapy

Successful Treatment of Patient With Ewing Sarcoma in the Setting of Inherited Cholestatic Liver Disease

Progressive familial intrahepatic cholestasis type 1 (PFIC1) is an inherited, progressive cholestatic liver disease. Here, we present an approach to the treatment of Ewing sarcoma in a patient with PFIC1. The diagnosis of PFIC1 presents a unique challenge in the treatment of Ewing sarcoma, as the standard-of-care vincristine, doxorubicin, cyclophosphamide/ifosfamide and etoposide chemotherapy backbone for Ewing sarcoma therapy treatment relies heavily on intact hepatic metabolism. In addition, we report prolonged lymphopenia and severe infectious complications in this patient, both of which may be attributed to more severe immunosuppression in setting of poor hepatic metabolism of chemotherapeutic agents.

Pharmacokinetics and dose adjustment of etoposide administered in a medium-dose etoposide, cyclophosphamide and total body irradiation regimen before allogeneic hematopoietic stem cell transplantation

BACKGROUND

We investigated the pharmacokinetics of etoposide (ETP) to reduce the inter-individual variations of ETP concentrations in patients with acute leukemia who underwent allogeneic hematopoietic stem cell transplantation. We also carried out an in vivo study using rats to verify the dose adjustment.

METHODS

This study included 20 adult patients. ETP was administered intravenously at a dose of 15 mg/kg once daily for 2 days (total dose: 30 mg/kg) combined with standard conditioning of cyclophosphamide and total body irradiation. In an in vivo study using rats, ETP was administered intravenously at a dose of 15 mg/kg or an adjusted dose. The ETP plasma concentration was determined by using HPLC. The pharmacokinetic parameters were estimated by using a 1-compartment model.

RESULTS

The peak concentration (Cmax) of ETP and the area under the plasma concentration-time curve (AUC) of ETP differed greatly among patients (range of Cmax, 51.8 - 116.5 μg/mL; range of AUC, 870 - 2015 μg · h/mL). A significant relationship was found between Cmax and AUC (R = 0.85, P < 0.05). Distribution volume (Vd) was suggested to be one of the factors of inter-individual variation in plasma concentration of ETP in patients (range of Vd, 0.13 - 0.27 L/kg), and correlated with Alb and body weight (R = 0.56, P < 0.05; R = 0.40, P < 0.05 respectively). We predicted Vd of rats by body weight of rats (with normal albumin levels and renal function), and the dose of ETP was adjusted using predicted Vd. In the dose adjustment group, the target plasma ETP concentration was achieved and the variation of plasma ETP concentration was decreased.

CONCLUSION

The results suggested that inter-individual variation of plasma concentration of ETP could be reduced by predicting Vd. Prediction of Vd is effective for reducing individual variation of ETP concentration and might enable a good therapeutic effect to be achieved.

Clinical and In Vitro Studies on Impact of High-Dose Etoposide Pharmacokinetics Prior Allogeneic Hematopoietic Stem Cell Transplantation for Childhood Acute Lymphoblastic Leukemia on the Risk of Post-Transplant Leukemia Relapse

The impact of etoposide (VP-16) plasma concentrations on the day of allogeneic hematopoietic stem cell transplantation (allo-HSCT) on leukemia-free survival in children with acute lymphoblastic leukemia (ALL) was studied. In addition, the in vitro effects of VP-16 on the lymphocytes proliferation, cytotoxic activity and on Th1/Th2 cytokine responses were assessed. In 31 children undergoing allo-HSCT, VP-16 plasma concentrations were determined up to 120 h after the infusion using the HPLC-UV method. For mentioned in vitro studies, VP-16 plasma concentrations observed on allo-HSCT day were used. In 84 % of children, VP-16 plasma concentrations (0.1-1.5 μg/mL) were quantifiable 72 h after the end of the drug infusion, i.e. when allo-HSCT should be performed. In 20 (65 %) children allo-HSCT was performed 4 days after the end of the drug infusion, and VP-16 was still detectable (0.1-0.9 μg/mL) in plasma of 12 (39 %) of them. Post-transplant ALL relapse occurred in four children, in all of them VP-16 was detectable in plasma (0.1-0.8 μg/mL) on allo-HSCT day, while there was no relapse in children with undetectable VP-16. In in vitro studies, VP-16 demonstrated impact on the proliferation activity of stimulated lymphocytes depending on its concentration and exposition time. The presence of VP-16 in plasma on allo-HSCT day may demonstrate an adverse effect on graft-versus-leukemia (GvL) reaction and increase the risk of post-transplant ALL relapse. Therefore, if 72 h after VP-16 administration its plasma concentration is still above 0.1 μg/mL then the postponement of transplantation for next 24 h should be considered to protect GvL effector cells from transplant material.

Pharmacokinetics of high-dose etoposide administered in combination with fractionated total-body irradiation as conditioning for allogeneic hematopoietic stem cell transplantation in children with acute lymphoblastic leukemia

Etoposide (VP-16) is one of the most widely used antitumor agents in pediatric oncology as well as chemotherapeutic agents used in conditioning regimen prior to allo-HSCT for childhood ALL. This study included 21 children with ALL who underwent allo-HSCT after conditioning with FTBI and high-dose of VP-16 (60 mg/kg) given intravenously as single four-h infusion on day -3 (n=2) or day -4 (n=19) prior to allo-HSCT. Blood samples were collected at defined time intervals until 120 h elapsed from the end of infusion. VP-16 plasma concentrations were determined using validated HPLC method. Three-compartment model was assumed for assessing PK parameters of VP-16. The median value of VP-16 C(max) measured at the end of infusion was 188.0 μg/mL (range 148.0-407.0 μg/mL). Out of 21 studied children, VP-16 was still detectable in 17 patients 72 h (median concentration 0.31 μg/mL) and in eight patients 96 h (median concentration 0.31 μg/mL) after the end of infusion. VP-16 concentration 96 h after the end of infusion was positively correlated with VP-16 AUC and negatively correlated with VP-16 CL normalized to body weight.

Camptothecin and podophyllotoxin derivatives: inhibitors of topoisomerase I and II - mechanisms of action, pharmacokinetics and toxicity profile

Camptothecins represent an established class of effective agents that selectively target topoisomerase I by trapping the catalytic intermediate of the topoisomerase I-DNA reaction, the cleavage complex. The water-soluble salt camptothecin-sodium - introduced in early trials in the 1960s - was highly toxic in animals, whereas the semisynthetic derivatives irinotecan and topotecan did not cause haemorrhagic cystitis because of their higher physicochemical stability and solubility at lower pH values. Myelosuppression, neutropenia and, to a lesser extent, thrombocytopenia are dose-limiting toxic effects of topotecan. In contrast to the structurally-related topotecan, irinotecan is a prodrug which has to be converted to SN-38, its active form. SN-38 is inactivated by conjugation, thus patients with Gilbert's syndrome and other forms of genetic glucuronidation deficiency are at an increased risk of irinotecan-induced adverse effects, such as neutropenia and diarrhoea. The cytotoxic mechanism of podophyllotoxin is the inhibition of topoisomerase II. Common adverse effects of etoposide include dose-limiting myelosuppression. Hypersensitivity reactions are more common with etoposide and teniposide than with etoposide phosphate because the formulations of the former contain sensitising solubilisers. Leukopenia and thrombocytopenia occur in 65% and 80%, respectively, of patients after administration of conventional doses of teniposide. Anorexia, vomiting and diarrhoea are generally of mild severity after administration of conventional doses of topoisomerase II inhibitors. Clinical pharmacokinetic studies have revealed substantial interindividual variabilities regarding the area under the concentration-time curve values and steady-state concentrations for all drugs reviewed in this article. Irinotecan, etoposide and teniposide are degraded via complex metabolic pathways. In contrast, topotecan primarily undergoes renal excretion. Regarding etoposide and teniposide, the extent of catechol formation over time during drug metabolism may be associated with a higher risk for secondary malignancies.

Pharmacokinetic Optimisation of Treatment with Oral Etoposide

Etoposide is a derivative of podophyllotoxin widely used in the treatment of several neoplasms, including small cell lung cancer, germ cell tumours and non-Hodgkin's lymphomas. Prolonged administration of etoposide aims for continuous inhibition of topoisomerase II, the intracellular target of etoposide, thus preventing tumour cells from repairing DNA breaks. However, the clinical advantages of extended schedules as compared with conventional short-term infusions remain unclear. Oral administration of etoposide represents the most feasible and economic strategy to maintain effective concentrations of drug for extended times. Nevertheless, the efficacy of oral etoposide therapy is contingent on circumventing pharmacokinetic limitations, mainly low and variable bioavailability. Inhibition of small bowel and hepatic metabolism of etoposide with specific cytochrome P450 inhibitors or inhibition of the intestinal P-glycoprotein efflux pump have been attempted to increase the bioavailability of oral etoposide, but the best results were obtained with daily oral administration of low etoposide doses (50-100 mg/day for 14-21 days). Saturable absorption of etoposide was reported for doses greater than 200 mg/day, whereas lower doses were associated with increased bioavailability, although they were characterised by high inter- and intrapatient variability. Pharmacokinetic parameters such as plasma trough concentration between two oral administrations (C(24,trough)), drug exposure time above a threshold value and area under the plasma concentration-time curve have been correlated with the pharmacodynamic effect of oral etoposide. Pharmacokinetic-pharmacodynamic relationships indicate that severe toxicity is avoided when peak plasma concentrations do not exceed 3-5 mg/L and C(24,trough) is under the threshold limit of 0.3 mg/L. To maintain effective etoposide plasma concentrations during prolonged oral administration, pharmacokinetic variability must be monitored in each patient, taking account of factors from many pharmacokinetic studies of etoposide, including absorption, distribution, protein binding, metabolism and elimination. Dosage reduction is generally useful to avoid haematological toxicity in patients with renal dysfunction (creatinine clearance <50 mL/min). The need for dosage adjustment based on liver function in patients with liver dysfunction is not completely defined, but generally is not indicated in patients with minor liver dysfunction. Adaptive dosage adjustment based on individual pharmacokinetic parameters, estimated using limited sampling strategies and population pharmacokinetic models, is more appropriate. This approach has been used with success in different clinical trials to increase the etoposide dosage, without significantly increasing toxicity. Various pharmacodynamic models have been proposed to guide etoposide oral dosage. However, they lack precision and accuracy and need to be refined by considering other predictor variables in order to extend their application in current clinical practice.

Population pharmacokinetics of high-dose etoposide in children receiving different conditioning regimens

Pharmacokinetics after high-dose (HD) etoposide (Eto) (40 mg/kg i.v. once as 4-h infusion, one patient 20 mg/kg i.v. as 4-h infusion, for 3 consecutive days) were studied in 31 children and young adults (age 0.8-23.7 years, median: 8.0 years) undergoing bone marrow transplantation after different conditioning regimens. Blood samples were collected until 97 h after the end of infusion. The population analysis of the first part of data (112 samples/21 patients, well documented) served to establish the pharmacokinetic model. The same data combined with the second part of data (50 samples/10 patients, 'intention to treat') then served to calculate the final population model. Data were best described by a three-compartment model with t1/2alpha = 0.28 h +/- 3.2%, t1/2beta = 3.6 h +/- 16.9% and t1/2gamma = 44.2 h +/- 56.5%, respectively (mean(geom) +/- CV(geom)). Clearance (CL) was 15.5 ml/min/m2 +/- 30.6% (mean(geom) +/- CV(geom)) and thus at the lower range of data reported in the literature. The fraction of unbound Eto (fu) was 7.0% (4.3-11.9%) [median (range)], with high intra-individual variability. An increase in f(u) with increasing total Eto was observed. The question of a principally lower Eto CL in children, as compared to adults, after HD treatment remains open.

Simulation tool for schedule-dependent etoposide exposure based on pharmacokinetic findings published in the literature

It is the aim of this study to establish a simulation tool for etoposide (Eto) which can be used to interpret drug monitoring data in clinical practice and to design new schedules for future protocols. As schedule dependency was observed for Eto, knowledge of concentration-time profiles is important. Pharmacokinetic data from children after low-dose i.v. administration of Eto together with data reported in the literature were used to construct the simulation tool. Validation was performed by independently reproducing various published data. Dose linearity of AUC was shown over the whole dose range of 20-2000 mg/m2 reported in the literature and fits the predictions by the simulation tool. There was no difference in clearance between children and adults. Close agreement was found between predicted and reported concentration-time profiles after various administration schedules. However, subgroups with significantly altered pharmacokinetics of Eto, such as patients with renal impairment or concurrent cisplatin chemotherapy, were excluded from the comparisons. In these patients values predicted for a 'regular' patient might be used as a base for possible dose modifications. In summary, a pharmacokinetic model of high predictive value is presented which allows simulations of Eto concentration-time profiles for low- as well as high-dose conditions and various infusion times.

Ultrafiltration and subsequent high performance liquid chromatography for in vivo determinations of the protein binding of etoposide

Etoposide is extensively (approximately 94%) bound to plasma proteins and the free non-protein-bound levels have been shown to correlate more closely to toxicity than total drug concentrations. A rapid and easily performed method, compared to the time consuming equilibrium dialysis, to obtain the free fraction is needed. The aim of this study was to evaluate ultrafiltration and subsequent high performance liquid chromatography (HPLC) for the determination of protein binding of etoposide. Spiked plasma from healthy, drug-free volunteers was used to compare ultrafiltration, using Amicon Centrifree filters, with equilibrium dialysis at 37 degrees C. The variability (CV) of the ultrafiltration method was 6.1 and 13.5% (n = 6) at 37 degrees C and room temperature (RT), respectively. The relative size of the free fraction obtained by ultrafiltration at 37 degrees C and RT was 1.22 (P = 0.0005) and 0.37 (P = 0.0001), respectively, compared with equilibrium dialysis at 37 degrees C. The chromatographic separation of metabolites from the mother compound when free etoposide is analyzed is crucial. It is shown that a hydroxy-acid metabolite of etoposide is quite dominant in a protein-free plasma fraction. The free concentrations were determined throughout a dose interval of 24 h in a patient receiving etoposide 100 mg/m2 daily. Ultrafiltration and subsequent HPLC is considered convenient and suitable for in vivo pharmacokinetic investigations.

Higher in vivo protein binding of etoposide in children compared with adult cancer patients

Etoposide is bound to plasma albumin (94%). Previous studies have revealed altered protein binding of etoposide in cancer patients. This has clinical implications since only the free fraction is considered pharmacologically active. We have studied the etoposide protein binding in 11 children (eight acute lymphocytic leukemia, two malignant histiocytosis, and one oligodendroglioma; age 1-17 years) and 46 adult patients (28 acute myelocytic leukemia, eight lymphoma, one multiple myeloma, and nine small cell lung cancer; age 38-81 years). All patients were treated with etoposide 50-200 mg/m2 i.v. or orally. Plasma from ten healthy volunteers, 26-50 years of age, was spiked with etoposide, 10 micrograms/ml, and the protein binding was compared with that in patient samples. The free etoposide concentration was determined by high performance liquid chromatography (HPLC) after ultrafiltration at room temperature. The free etoposide fraction was lower, 2.5 +/- 0.6% (mean +/- SD), in the children compared with 5.0 +/- 3.6% in adult cancer patients. In plasma from healthy adults it was 3.2 +/- 0.3%. It is concluded that children have significantly lower levels of free etoposide compared with adult patients (P = 0.03) as well as with healthy subjects (P = 0.001), which is likely to affect metabolism and renal clearance as well as cellular uptake of the drug.

The pharmacokinetics and toxicity of two application schedules with high-dose VP-16 in patients receiving an allogeneic bone marrow transplantation

BACKGROUND

Etoposide is one of the few drugs being used in conditioning regimens because of the ease with which its dosage can be escalated by a factor of 6 compared to the normal dose. The best schedule in high-dose chemotherapy is not known.

PATIENTS AND METHODS

We evaluated the pharmacokinetics (PK) of high-dose VP-16 during two different schedules (6-hour and 3 x 1-hour infusions) and the toxicity of the two application modes in patients with leukemia who underwent allogeneic bone marrow transplantation.

RESULTS

A significant difference (p = 0.008) in the volume of distribution at steady state was observed. The mean Vss was 0.21 L/kg in the 6-hour group and 0.36 in the 3 x 1-hour group. The total drug exposure time with plasma levels > 100 ng/ml is significantly longer in the 'split' group (74 vs. 143 h). Other PK parameters such as plasma clearance and area under the curve were not significantly different. Leukocyte recovery to WBC levels > 0.2 and > 0.5/nl as well as platelet recovery to stable counts > 50/nl was significantly (p = 0.002, 0.009 and 0.04) prolonged in the 'split' group (3.7 vs. 12.3, 8.3 vs. 14.3 and 25 vs. 35 d). The liver toxicity as indicated by bilirubin peak levels was significantly (p = 0.02) more severe in the 'split' group (1.7 vs. 5.4 mg/dl).

CONCLUSION

The area under the curve as a measure of total drug exposure cannot be correlated to the observed higher toxicity in the patient group with the 'split' application mode. The drug exposure time as well as the three high peak plasma levels may be more important.

Pharmacokinetics and pharmacodynamics of 21-day continuous oral etoposide in pediatric patients with solid tumors

PURPOSE

The objectives of this study were to determine etoposide pharmacokinetics during continuous low-dose oral administration to children with solid tumors and to evaluate the relationships between parameters of etoposide systemic exposure and toxicity.

PATIENTS AND METHODS

In this phase I study, children were administered oral etoposide (25 to 75 mg/m2/day) for 21 days as a diluted solution of the intravenous preparation, divided into three equal daily doses. Plasma pharmacokinetics were studied on day 1 of therapy in 18 children and again on day 21 in 14 of these children. Etoposide plasma concentration-time data were fitted to a first-order absorption, two-compartment model with use of bayesian estimation. Pharmacokinetic parameter estimates from day 1 were used to estimate steady-state etoposide systemic exposure in all children. Stepwise multivariate regression was used in an exploratory manner to determine patient, laboratory, or pharmacokinetic predictors of toxicity.

RESULTS

Although there was substantial intrapatient variability, there was no difference in the area under the concentration-time curve [AUC(0-8hr)] measured at day 21 compared with the steady-state AUC(0-8hr) estimated from day 1 pharmacokinetic parameters (p = 0.64). Degree of neutropenia was best predicted by the estimated duration that steady-state plasma etoposide concentrations were maintained above 1 microgram/ml (t > 1 microgram/ml) rather than peak plasma concentrations, AUC(0-8hr), dosage, or other patient characteristics. Assuming a bioavailability of the oral solution of approximately 50%, the median etoposide systemic clearance was 21.4 ml/min/m2, a value similar to clearance estimates after intravenous etoposide in pediatric populations.

CONCLUSION

We conclude that a parameter reflective of etoposide systemic exposure (t > 1 microgram/ml) correlates more strongly with neutropenia than does dosage or other patient characteristics.

Etoposide protein binding in cancer patients

The protein binding of etoposide was studied in vivo in 36 cancer patients receiving etoposide therapy. Free etoposide was separated from plasma using an ultrafiltration method and the etoposide concentrations (free and total) were measured by high-performance liquid chromatography (HPLC). Considerable interpatient variation in the protein binding of etoposide was observed. The protein binding of etoposide varied from 80% to 97% (mean, 93%). Univariate analysis showed a significant inverse correlation between the free fraction of etoposide and serum albumin (r = 0.74), daily dose (r = 0.37) and age (r = -0.34). Multivariate analysis demonstrated that serum albumin and age were independent predictors of the etoposide free fraction. Serum bilirubin showed no correlation with etoposide protein binding. There is wide variation in etoposide protein binding in cancer patients, which is mostly dependent on serum albumin concentration.

Use of etoposide in patients with organ dysfunction: pharmacokinetic and pharmacodynamic considerations

Etoposide is a podophyllotoxin deriverative with activity against a wide variety of malignancies. It is also used in many clinical conditions in which renal or hepatic function is impaired. To establish a basis for making initial dose adjustments in patients with renal or hepatic dysfunction, the clinical pharmacology (e.g., absorption, distribution, protein binding, metabolism, and elimination) of etoposide is presented. Studies of the use of etoposide in patients with renal or hepatic dysfunction are summarized. The importance of protein binding to etoposide disposition, especially in patients with hepatic dysfunction is discussed. Pharmacodynamics refers to the relationship between drug concentration at the site of action (receptor) and pharmacologic response (toxicity or efficacy). The pharmacodynamics of etoposide has been studied in only a few patients with renal and (or) hepatic dysfunction and must be studied in larger populations before definitive dosing guidelines can be recommended. However, some general initial dosing recommendations for the use of etoposide in patients with renal and hepatic dysfunction are presented.