Etoposide protein binding in cancer patients

Selective fluorescence turn-on detection of combination cisplatin-etoposide chemotherapy based on N-CDs/GSH-CuNCs nanoprobe

Cisplatin (CIS) and etoposide (ETP) combination therapy is highly effective for treating various cancers. However, the potential for pharmacokinetic interactions between these drugs necessitates selective sensing methods to quantitate both CIS and ETP levels in patient's plasma. This work develops a dual fluorescence probe strategy using glutathione-capped copper nanoclusters (GSH-CuNCs) and nitrogen-doped carbon dots (N-CDs) for the simultaneous analysis of CIS and ETP. The fluorescence signal of GSH-CuNCs at 615 nm increased linearly with CIS concentration while the N-CD emission at 480 nm remained unaffected. Conversely, the N-CD fluorescence was selectively enhanced by ETP with no interference with the CuNC fluorescence. Extensive materials characterization including UV-vis, fluorescence spectroscopy, XRD, and TEM confirmed the synthesis of the nanoprobes. The sensor showed high sensitivity with limits of detection of 6.95 ng mL-1 for CIS and 7.63 ng mL-1 for ETP along with excellent selectivity against potential interferences in rabbit plasma. Method feasibility was demonstrated with application to real rabbit plasma samples. The method was further applied to estimate the pharmacokinetic parameters of CIS before and after ETP coadministration. The dual nanoprobe sensing strategy enables rapid and selective quantitation of CIS and ETP levels to facilitate therapeutic drug monitoring and optimization of combination chemotherapy regimens.

Effect of Moderate Malnutrition on the Pharmacokinetics of Etoposide and Vincristine in Freshly Weaned Rats

BACKGROUND

Moderate malnutrition is a common problem in young children. It is observed that severe malnutrition affects the pharmacokinetics of chemotherapy drugs in pediatric cancer patients, but moderate malnutrition is not well studied in this context.

OBJECTIVES

In this study, we aimed to understand how moderate malnutrition affects the pharmacokinetics of two chemotherapy drugs, etoposide and vincristine, using a murine model of early age moderate malnutrition.

METHODS

We developed a murine model of moderate childhood malnutrition by subjecting freshly weaned Sprague-Dawley rats to 8% protein diet for 8 weeks. In two separate experiments, we administered etoposide and vincristine (N = 8 for etoposide and N = 12 for vincristine each in protein deficient and control groups) through tail vein injection for pharmacokinetics study.

RESULTS

We found ~ 60% increase in area under the concentration-time curve (AUC) of etoposide in malnourished animals as compared to well-nourished animals. Furthermore, clearance, volume of distribution, and half-life were decreased by ~ 37, 53, and 24%, respectively, in malnourished animals. Pharmacokinetic parameters of vincristine showed only marginal differences between well-nourished and malnourished groups.

CONCLUSIONS

Our results suggest that while moderate malnutrition significantly affects the pharmacokinetics of etoposide, pharmacokinetics of vincristine remain unchanged. Since chemotherapy drugs have a narrow therapeutic index, the difference in AUC observed in our study might explain the increased toxicity of etoposide in malnourished pediatric cancer patients. This brings forth a need for robust clinical studies to validate our findings and optimize dose for malnourished patients.

Photochemical Internalization of Etoposide Using Dendrimer Nanospheres Loaded with Etoposide and Protoporphyrin IX on a Glioblastoma Cell Line

Glioblastoma multiforme (GBM) is the most common malignant primary neoplasm of the adult central nervous system originating from glial cells. The prognosis of those affected by GBM has remained poor despite advances in surgery, chemotherapy, and radiotherapy. Photochemical internalization (PCI) is a release mechanism of endocytosed therapeutics into the cytoplasm, which relies on the membrane disruptive effect of light-activated photosensitizers. In this study, phototherapy by PCI was performed on a human GBM cell-line using the topoisomerase II inhibitor etoposide (Etop) and the photosensitizer protoporphyrin IX (PpIX) loaded in nanospheres (Ns) made from generation-5 polyamidoamine dendrimers (PAMAM(G5)). The resultant formulation, Etop/PpIX-PAMAM(G5) Ns, measured 217.4 ± 2.9 nm in diameter and 40.5 ± 1.3 mV in charge. Confocal microscopy demonstrated PpIX fluorescence within the endo-lysosomal compartment, and an almost twofold increase in cellular uptake compared to free PpIX by flow cytometry. Phototherapy with 3 min and 5 min light illumination resulted in a greater extent of synergism than with co-administered Etop and PpIX; notably, antagonism was observed without light illumination. Mechanistically, significant increases in oxidative stress and apoptosis were observed with Etop/PpIX-PAMAM(G5) Ns upon 5 min of light illumination in comparison to treatment with either of the agents alone. In conclusion, simultaneous delivery and endo-lysosomal co-localization of Etop and PpIX by PAMAM(G5) Ns leads to a synergistic effect by phototherapy; in addition, the finding of antagonism without light illumination can be advantageous in lowering the dark toxicity and improving photo-selectivity.

Focused Ultrasound-Mediated Blood-Brain Barrier Opening Increases Delivery and Efficacy of Etoposide for Glioblastoma Treatment

PURPOSE

Glioblastoma (GBM) is a devastating disease. With the current treatment of surgery followed by chemoradiation, outcomes remain poor, with median survival of only 15 months and a 5-year survival rate of 6.8%. A challenge in treating GBM is the heterogeneous integrity of the blood-brain barrier (BBB), which limits the bioavailability of systemic therapies to the brain. There is a growing interest in enhancing drug delivery by opening the BBB with the use of focused ultrasound (FUS). We hypothesize that an FUS-mediated BBB opening can enhance the delivery of etoposide for a therapeutic benefit in GBM.

METHODS AND MATERIALS

A murine glioma cell line (Pdgf⁺, Pten^-/-, P53^-/-) was orthotopically injected into B6(Cg)-Tyrc-2J/J mice to establish the syngeneic GBM model for this study. Animals were treated with FUS and microbubbles to open the BBB to enhance the delivery of systemic etoposide. Magnetic resonance (MR) imaging was used to evaluate the BBB opening and tumor progression. Liquid chromatography tandem mass spectrometry was used to measure etoposide concentrations in the intracranial tumors.

RESULTS

The murine glioma cell line is sensitive to etoposide in vitro. MR imaging and passive cavitation detection demonstrate the safe and successful BBB opening with FUS. The combined treatment of an FUS-mediated BBB opening and etoposide decreased tumor growth by 45% and prolonged median overall survival by 6 days: an approximately 30% increase. The FUS-mediated BBB opening increased the brain tumor-to-serum ratio of etoposide by 3.5-fold and increased the etoposide concentration in brain tumor tissue by 8-fold compared with treatment without ultrasound.

CONCLUSIONS

The current study demonstrates that BBB opening with FUS increases intratumoral delivery of etoposide in the brain, resulting in local control and overall survival benefits.

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.

Transdermal Delivery of Etoposide Phosphate I: In Vitro and In Vivo Evaluation

Cancer chemotherapy frequently requires long periods of multiple intravenous infusions that often results in patients opting out of treatment. The main purpose of this study was to investigate the feasibility of delivering one of these anticancer agents: etoposide phosphate (ETP) transdermally using iontophoresis and a combination of iontophoresis/microporation. The iontophoresis conditions for ETP were first optimized in vitro then tested in vivo in a rabbit model. Both ETP and its active form etoposide (VP) were quantified in dermis (via microdialysis sampling) and in plasma, with a specially developed high-performance liquid chromatography method. In vitro, the amount of total etoposide permeated and the steady state flux increased (p < 0.05) with increase in iontophoretic current densities (100-400 μA/cm(2)). At 300 μA/cm(2), microporation/iontophoresis further improved both parameters by 2- and 2.8-fold, respectively. In vivo, exposure increased proportionally to current density in plasma, whereas dermal concentration dropped significantly at the highest current density. Microporation led to a 50% increase in Cmax and AUClast values in both skin and plasma. In conclusion, a mild current density (300 μA/cm(2)) and a small surface area (10.1 cm(2)) achieved and maintained the minimum effective concentration for the entire duration of electrical current delivery; microporation further increased the plasma concentrations at the same current density.

Resistance to cancer chemotherapy: failure in drug response from ADME to P-gp

Cancer chemotherapy resistance (MDR) is the innate and/or acquired ability of cancer cells to evade the effects of chemotherapeutics and is one of the most pressing major dilemmas in cancer therapy. Chemotherapy resistance can arise due to several host or tumor-related factors. However, most current research is focused on tumor-specific factors and specifically genes that handle expression of pumps that efflux accumulated drugs inside malignantly transformed types of cells. In this work, we suggest a wider and alternative perspective that sets the stage for a future platform in modifying drug resistance with respect to the treatment of cancer.

Clinical pharmacology in the adolescent oncology patient

Numerous studies have documented that adolescents and young adults (AYAs) experience a significant cancer burden as well as significant cancer mortality compared with other age groups. The reasons for the disparate outcomes of AYAs and other age groups are not completely understood and are likely to be multifactorial, including a range of sociodemographic issues unique to these individuals as well as differences between adolescents, younger pediatric patients, and adults in the pharmacology of anticancer agents. Because adolescence is a period of transition from childhood to early adulthood, numerous physical, physiologic, cognitive, and behavioral changes occur during this time. In this review, we provide an overview of the unique developmental physiology of the adolescent and explain how these factors and the behavioral characteristics of adolescents may affect the pharmacology of anticancer agents in this patient population. Finally, we describe examples of studies that have assessed the relation between drug disposition and age, focusing on the AYA age group.

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.

Population Pharmacokinetic-Pharmacodynamic Model for Neutropenia with Patient Subgroup Identification: Comparison across Anticancer Drugs

PURPOSE

Cancer chemotherapy, although based on body surface area, often causes unpredictable myelosuppression, especially severe neutropenia. The aim of this study was to evaluate qualitatively and quantitatively the influence of patient-specific characteristics on the neutrophil concentration-time course, to identify patient subgroups, and to compare covariates on system-related pharmacodynamic variable between drugs.

EXPERIMENTAL DESIGN

Drug and neutrophil concentration, demographic, and clinical chemistry data of several trials with docetaxel (637 patients), paclitaxel (45 patients), etoposide (71 patients), or topotecan (191 patients) were included in the covariate analysis of a physiology-based pharmacokinetic-pharmacodynamic neutropenia model. Comparisons of covariate relations across drugs were made.

RESULTS

A population model incorporating four to five relevant patient factors for each drug to explain variability in the degree and duration of neutropenia has been developed. Sex, previous anticancer therapy, performance status, height, binding partners, or liver enzymes influenced system-related variables and alpha1-acid glycoprotein, albumin, bilirubin, concomitant cytotoxic agents, or administration route changed drug-specific variables. Overall, female and pretreated patients had a lower baseline neutrophil concentration. Across-drug comparison revealed that several covariates (e.g., age) had minor (clinically irrelevant) influences but consistently shifted the pharmacodynamic variable in the same direction.

CONCLUSIONS

These mechanistic models, including patient characteristics that influence drug-specific parameters, form the rationale basis for more tailored dosing of individual patients or subgroups to minimize the risk of infection and thus might contribute to a more successful therapy. In addition, nonsignificant or clinically irrelevant relations on system-related parameters suggest that these covariates could be negligible in clinical trails and daily use.

Biliary excretion of etoposide in children with cancer

PURPOSE

Two children with soft tissue sarcomas receiving etoposide as part of their standard clinical treatment had external biliary drainage due to obstruction of the bile duct. These unusual cases provided an opportunity to investigate the biliary clearance of etoposide by determining etoposide concentrations in bile and plasma samples obtained during chemotherapy.

PATIENTS AND METHODS

Etoposide was administered to patient 1 at a dose of 150 mg/m(2), as a 4 h infusion, on each of three days of treatment. Patient 2 received a daily etoposide dose of 800 mg/m(2) as a 24 h continuous infusion, also over a 3-day treatment period. Bile and plasma samples were obtained at regular intervals from both patients and etoposide levels quantified by LC/MS analysis.

RESULTS AND DISCUSSION

Biliary etoposide clearance was approximately equal to the flow of bile, with an average clearance of 0.32 ml/min determined in patient 1. Less than 2% of the etoposide dose administered was excreted in the bile in either patient studied, indicating that biliary clearance of etoposide is relatively minor. These results suggest that etoposide dose adjustment is unnecessary in patients with biliary obstruction.

Plasma etoposide catechol increases in pediatric patients undergoing multiple-day chemotherapy with etoposide

PURPOSE

The purpose of this research was to determine inter- and intrapatient differences in the pharmacokinetic profiles of etoposide and its genotoxic catechol metabolite during conventional multiple-day dosing of etoposide in pediatric patients.

EXPERIMENTAL DESIGN

Seven pediatric patients with various malignancies received etoposide at a dose of 100 mg/m(2) i.v. over 1 h daily for 5 days. Blood samples were taken at selected time points on days 1 and 5. Plasma and protein-free plasma concentrations of etoposide and etoposide catechol were determined using a validated liquid chromatography/tandem mass spectrometry assay. Pharmacokinetic parameters of both etoposide and etoposide catechol were calculated using the WinSAAM modeling program developed at NIH.

RESULTS

The mean maximum concentration (C(max)) for total (0.262 +/- 0.107 micro g/ml) and free catechol (0.0186 +/- 0.0082 micro g/ml) on day 5 were higher than the mean C(max) for total (0.114 +/- 0.028 micro g/ml) and free catechol (0.0120 +/- 0.0091 micro g/ml) on day 1. The mean area under the plasma concentration-time curve (AUC)(24h) for total (105.4 +/- 49.1 micro g.min/ml) and free catechol (4.89 +/- 2.23 micro g x min/ml) on day 5 were much greater (P < 0.05) than those for total (55.9 +/- 16.1 micro g x min/ml) and free catechol (3.04 +/- 1.04 micro g x min/ml) on day 1. In contrast, the AUC(24h) for etoposide was slightly lower on day 5 than on day 1.

CONCLUSIONS

The C(max) and AUC(24h) for etoposide catechol were significantly higher on day 5 than on day 1. This suggests that metabolism of etoposide to its catechol metabolite increases in pediatric patients receiving multiple-day bolus etoposide infusions. These findings may be relevant to future reduction of the risk of leukemia as a treatment complication, because etoposide and etoposide catechol are both genotoxins.

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.

Simultaneous determination of etoposide and its catechol metabolite in the plasma of pediatric patients by liquid chromatography/tandem mass spectrometry

The anticancer drug etoposide is associated with leukemias with MLL gene translocations and other translocations as a treatment complication. The genotype of cytochrome P450 3A4 (CYP3A4), which converts etoposide to its catechol metabolite, influences the risk. In order to perform pharmacokinetic studies aimed at further elucidation of the translocation mechanism, we have developed and validated a liquid chromatography/electrospray/tandem mass spectrometry assay for the simultaneous analysis of etoposide and its catechol metabolite in human plasma. The etoposide analog teniposide was used as the internal standard. Liquid chromatography was performed on a YMC ODS-AQ column. Simultaneous determination of etoposide and its catechol metabolite was achieved using a small volume of plasma, so that the method is suitable for pediatric patients. The limits of detection were 200 ng ml(-1) etoposide and 10 ng ml(-1) catechol metabolite in human plasma and 25 ng ml(-1) etoposide and 2.5 ng ml(-1) catechol metabolite in protein-free plasma, respectively. Acceptable precision and accuracy were obtained for concentrations in the calibration curve ranges 0.2--100 microg ml(-1) etoposide and 10--5000 ng ml(-1) catechol metabolite in human plasma. Acceptable precision and accuracy for protein-free human plasma in the range 25--15 000 ng ml(-1) etoposide and 2.5--1500 ng ml(-1) etoposide catechol were also achieved. This method was selective and sensitive enough for the simultaneous quantitation of etoposide and its catechol as a total and protein-free fraction in small plasma volumes from pediatric cancer patients receiving etoposide chemotherapy. A pharmacokinetic model has been developed for future studies in large populations.

Determination of etoposide in human plasma and leukemic cells by high-performance liquid chromatography with electrochemical detection

This paper describes a high-performance liquid chromatographic method with electrochemical detection for the determination of etoposide levels in plasma, total and non-protein bound concentration, and in leukemic cells. The precision for between-runs (n=6) was 7.0, 4.9, and 9.5%, the accuracy was 3.7, 7.1 and 6.3%, and within-runs precision (n=6) was 3.9, 2.9 and 5.1% for total plasma, non-protein bound plasma fraction and leukemic cells, respectively. The correlation coefficients (R2) were 1.00 for all calibration curves. These assays have been applied to analyze samples from one patient with acute myelogenous leukemia during 24 h after i.v. infusion of etoposide (100 mg/m2).

Pharmacokinetics of anticancer agents in patients with impaired liver function

This report reviews published information on the clinical pharmacokinetics of antitumour agents in patients with liver dysfunction, associated with primary liver disease or liver metastases. Information was available for anthracyclines and their related compounds, antimetabolites, cyclophosphamide, vinca alkaloids, taxanes and epipodophyllotoxins. Changes in the pharmacokinetic profile or metabolism in patients with mild or severe hepatobiliary dysfunction are described and the relationships between serum levels, parameters employed for measuring hepatic function and toxic or therapeutic effects are examined. Current knowledge of the pharmacokinetics of antineoplastic agents in liver disease is far from complete, mostly obtained in small numbers of non-homogeneous patients often presenting only moderate liver dysfunction, and empirical guidelines for dose assessment are still largely applied in clinical practice. Because of the complex pathophysiological mechanisms of liver insufficiency in cancer patients, there is still doubt whether endogenous markers are useful. Although caution in treating cancer patients with liver insufficiency is compulsory, for most compounds there seems no need to recommend dose reductions for moderate impairment. However, for the tubulin acting agents, vincristine, vinblastine and possibly for paclitaxel and docetaxel, there is strong evidence that dose adjustment is mandatory in order to avoid excessive neutropenia and neurotoxicity.

Determination of the cytotoxic catechol metabolite of etoposide (3'O-demethyletoposide) in human plasma by high-performance liquid chromatography

The anticancer drug etoposide undergoes O-demethylation in humans. The formed catechol metabolite exhibits significant cytotoxic activity. A simple, rapid, selective, and sensitive reversed-phase high-performance liquid chromatography assay was developed for the measurement of etoposide catechol in plasma of tumour patients. The metabolite was quantified using electrochemical detection. Ascorbic acid was added to each sample to prevent oxidation of etoposide catechol during sample preparation. Linear responses were obtained between 40 ng/ml and 1.25 microg/ml with correlation coefficients exceeding 0.991. The detection limit was 10 ng/ml. Recovery, within-day precision, between-day precision and accuracy were satisfactory. The method has been applied to characterize the concentration-time profile of etoposide catechol in plasma of tumour patients following administration of high-dose etoposide.

Randomized comparison of etoposide pharmacokinetics after oral etoposide phosphate and oral etoposide

Etoposide phosphate is a water-soluble prodrug of etoposide. The plasma pharmacokinetics of etoposide following oral administration of etoposide phosphate or oral etoposide were compared. Seventeen patients with solid tumours were enrolled to receive oral etoposide phosphate 125 mg m(-2) on days 1-5 every 3 weeks, with escalation to 175 mg m(-2) from course 3 when possible. Patients were randomized to receive oral etoposide phosphate or oral etoposide on day 1 of course 1 and the alternative compound on day 1 of course 2. Fifteen patients received two or more courses and were evaluable for pharmacokinetic comparisons. The median AUC(inf) (area under the concentration vs time curve from zero to infinity) of etoposide was 77.7 mg l(-1) h after etoposide phosphate (95% CI 61.3-100.5) and 62.0 mg l(-1) h after oral etoposide (95% CI 52.2-76.9). The difference in favour of etoposide phosphate was borderline significant: median 9.9 mg l(-1) h (95% CI 0.1-32.8 mg l(-1) h; P = 0.05). However, the inter-patient variability of etoposide AUC(inf) was not improved (coefficients of variation 42.3% and 48.4%). Etoposide phosphate was undetectable in plasma after oral administration. Toxicities of oral etoposide phosphate were not different from those known for etoposide. In conclusion, oral etoposide phosphate does not offer a clinically relevant benefit over oral etoposide.