Changes in the clearance of total and unbound etoposide in patients with liver dysfunction

Revisiting the outstanding questions in cancer nanomedicine with a future outlook

The field of cancer nanomedicine has been fueled by the expectation of mitigating the inefficiencies and life-threatening side effects of conventional chemotherapy. Nanomedicine proposes to utilize the unique nanoscale properties of nanoparticles to address the most pressing questions in cancer treatment and diagnosis. The approval of nano-based products in the 1990s inspired scientific explorations in this direction. However, despite significant progress in the understanding of nanoscale properties, there are only very few success stories in terms of substantial increase in clinical efficacy and overall patient survival. All existing paradigms such as the concept of enhanced permeability and retention (EPR), the stealth effect and immunocompatibility of nanomedicine have been questioned in recent times. In this review we critically examine impediments posed by biological factors to the clinical success of nanomedicine. We put forth current observations on critical outstanding questions in nanomedicine. We also provide the promising side of cancer nanomedicine as we move forward in nanomedicine research. This would provide a future direction for research in nanomedicine and inspire ongoing investigations.

Pharmacokinetic and Pharmacogenetic Study of Etoposide in High-Dose Protocol (TI-CE) for Advanced Germ Cell Tumors

BACKGROUND

Etoposide dosing is based on body surface area. We evaluated if further dose individualization would be required for high dose (HD) etoposide within the TI-CE (taxol, ifosfamide, carboplatin, and etoposide) protocol.

METHODS

Eighty-eight patients received 400 mg/m²/day of etoposide as a 1-hour IV infusion on 3 consecutive days over 3 cycles as part of a phase II trial evaluating efficacy of therapeutic drug monitoring (TDM) of carboplatin in the TI-CE HD protocol. Pharmacokinetic (PK) data were analyzed using population PK model on NONMEM to quantify inter- and intra-individual variabilities. Relationship between etoposide exposure and pharmacodynamic (PD) endpoints, and between selected genetic polymorphisms and tumor response or toxicity were evaluated.

RESULTS

The inter-patient, inter- and intra-cycle variabilities of clearance were 16%, 9% and 0.1%, respectively. The PK-PD relationship was not significant despite a trend toward higher etoposide exposure in patients responding to treatment. A significant correlation was found between exposure and extended neutropenia at cycle 3. A significant association between UGT1A1*28 polymorphism and late neutropenia was observed but needs further evaluation.

CONCLUSIONS

The present study suggests that neither a priori dose individualization nor dose adaptation using TDM is required validating body surface area dosing of etoposide in the TI-CE protocol.

Therapeutic effect of N-acetylcysteine on chemotherapy-induced liver injury

BACKGROUND

N-acetylcysteine (NAC) may be useful in the management of chemotherapy-induced liver injury.

AIMS

The present study evaluates the possible therapeutic effects of NAC on chemotherapy-induced hepatotoxicity.

METHODS

A total of 102 patients' files who were diagnosed with cancer between 2015 and 2019 were evaluated retrospectively. Two patient groups with and without NAC were selected. NAC was administered in a 3-μg/kg IV dose in a 24-h infusion to 70 patients when any alanine aminotransferase (ALT) or gamma-glutamyl transferase (GGT) values reached three times the normal levels. The other group consisted of 32 patients who were not treated with NAC. Alanine aminotransferase and GGT values were recorded at pretreatment, and on the 1st, 3rd, 5th, and 7th days in both the NAC and non-NAC groups from files.

RESULTS

In the NAC group, ALT and GGT values on day 1, 3, 5, and 7 differed from each other, decreasing from day 1 to day 7. A statistically significant difference was noted between the values in the NAC group (p < 0.001). In the non-NAC group, the ALT values on day 7 were lower than the ALT values on day 1. A comparison of the ALT and GGT values in the NAC and non-NAC groups found that the values in the NAC group decreased earlier than in the non-NAC group.

CONCLUSIONS

This study shows that NAC has a therapeutic effect on hepatotoxicity in children being treated with chemotherapeutic agents due to underlying malign diseases. The early reduction in the results of liver function tests is important for the continuation of chemotherapy.

Recommendations for the Use of Etoposide-Based Therapy and Bone Marrow Transplantation for the Treatment of HLH: Consensus Statements by the HLH Steering Committee of the Histiocyte Society

Hemophagocytic lymphohistiocytosis (HLH) is a life-threatening hyperinflammatory syndrome requiring aggressive immunosuppressive therapy. Following 2 large international studies mainly targeting pediatric patients with familial disease and patients without underlying chronic or malignant disease, the HLH-94 protocol is recommended as the standard of care when using etoposide-based therapy by the Histiocyte Society. However, in clinical practice, etoposide-based therapy has been widely used beyond the study inclusion criteria, including older patients and patients with underlying diseases (secondary HLH). Many questions remain around these extended indications and published reports do not address several practical issues. To tackle these concerns, the HLH Steering Committee of the Histiocyte Society decided to issue guidance for use of the HLH-94 protocol. The group convened in a structured consensus finding process to define recommendations that are based largely on expert opinion backed up by available data from the literature. The recommendations address all main elements of HLH-94 including corticosteroids, cyclosporin, etoposide, intrathecal therapy, and hematopoietic stem cell transplantation (HSCT) and consider various forms of HLH and all age groups. Aspects covered include indications, applications, dosing, side effects, duration of therapy, salvage therapy, and HSCT. These recommendations aim to provide a framework to guide treatment decisions in this severe disease.

Translational studies of phenotypic probes for the mononuclear phagocyte system and liposomal pharmacology

As nanoparticles (NPs) are cleared via phagocytes of the mononuclear phagocyte system (MPS), we hypothesized that the function of circulating monocytes and dendritic cells (MO/DC) in blood can predict NP clearance (CL). We measured MO/DC phagocytosis and reactive oxygen species (ROS) production in mice, rats, dogs, and patients with refractory solid tumors. Pharmacokinetic studies of polyethylene glycol (PEG)-encapsulated liposomal doxorubicin (PEGylated liposomal doxirubicin [PLD]), CKD-602 (S-CKD602), and cisplatin (SPI-077) were performed at the maximum tolerated dose. MO/DC function was also evaluated in patients with recurrent epithelial ovarian cancer (EOC) administered PLD. Across species, a positive association was observed between cell function and CL of PEGylated liposomes. In patients with EOC, associations were observed between PLD CL and phagocytosis (R(2) = 0.43, P = 0.04) and ROS production (R(2) = 0.61, P = 0.008) in blood MO/DC. These findings suggest that probes of MPS function may help predict PEGylated liposome CL across species and PLD CL in patients with EOC.

Model-based neutrophil-guided dose adaptation in chemotherapy: evaluation of predicted outcome with different types and amounts of information

One of the most employed approaches to reduce severe neutropenia following anticancer drug regimens is to reduce the consecutive dose in fixed steps, commonly by 25%. Another approach has been to use pharmacokinetic (PK) sampling to tailor dosing, but only rarely have model-based computer approaches utilizing collected PK and/or pharmacodynamic (PD) data been used. A semi-mechanistic model for myelosuppression that can characterize the interindividual and interoccasion variability in the time-course of neutrophils following administration of a wide range of anticancer drugs may be used in a clinical setting for model-based dose individualization. The aim of this study was to compare current stepwise procedures to model-based dose adaptation by simulations, and investigate if the overall dose intensity in the population could be increased without increasing the risk of severe toxicity. The value of various amounts of PK- and/or PD-information was compared to standard dosing strategies using a maximum a posteriori procedure in NONMEM. The results showed that when information on neutrophil counts was available, the additional improvement from PK sampling was negligible. Using neutrophil sampling at baseline and an observation near the predicted nadir increased the number of patients in the target range by 27% in comparison with a one-sided 25% dose adjustment schedule, while keeping the number of patients experiencing severe toxicity at a comparable low level after five courses of treatment. High interindividual variability did not limit the benefit of model-based dose adaptation, whereas high interoccasion variability was predicted to make any dose adaptation method less successful. This study indicates that for successful model-based dose adaptation clinically, there is no need for drug concentration sampling, and that one extra neutrophil measurement in addition to the pre-treatment value is sufficient to limit severe neutropenia while increasing dose intensity.

A tool for neutrophil guided dose adaptation in chemotherapy

Chemotherapy dosing in anticancer treatment is a balancing act between achieving concentrations that are effective towards the malignancy and that result in acceptable side-effects. Neutropenia is one major side-effect of many antitumor agents, and is related to an increased risk of infection. A model capable of describing the time-course of myelosuppression from administered drug could be used in individual dose selection. In this paper we describe the transfer of a previously developed semi-mechanistic model for myelosuppression from NONMEM to a dosing tool in MS Excel, with etoposide as an example. The tool proved capable to solve a differential equation system describing the pharmacokinetics and pharmacodynamics, with estimation performance comparable to NONMEM. In the dosing tool the user provides neutrophil measures from a previous treatment course and request for the dose that results in a desired nadir in the upcoming course through a Bayesian estimation procedure.

Pharmacokinetic modulation of oral etoposide by ketoconazole in patients with advanced cancer

PURPOSE

Etoposide is a widely used cytotoxic drug that is commercially available in both intravenous and oral formulations. High interpatient pharmacokinetic variability has been associated with oral etoposide administration. Various strategies used in the past to reduce such variability have not been successful. Hence, this study was designed to evaluate if pharmacokinetic modulation of oral etoposide with ketoconazole could lead to a favorable alteration of etoposide pharmacokinetics, and to assess the feasibility and safety of this approach.

METHODS

Thirty-two patients were treated with ketoconazole 200 mg daily with an escalating dose of oral etoposide starting at a dose of 50 mg every other day. Pharmacokinetic samples were obtained during the first treatment cycle after the administration of an oral etoposide and ketoconazole dose. Additional baseline pharmacokinetic studies of etoposide alone were performed 4 days prior to the first treatment cycle.

RESULTS

Dose limiting toxicities were neutropenia and fatigue. Ketoconazole increased the area under the plasma concentration-time curve (AUC) of oral etoposide by a median of 20% (p < 0.005). Ketoconazole did not reduce the interpatient variability in etoposide pharmacokinetics. Pretreatment bilirubin levels correlated with etoposide clearance (Spearman's r = -0.48, p = 0.008). The maximum tolerated dose was etoposide administered at 50 mg daily and ketoconazole 200 mg qd for 3 of 5 weeks.

CONCLUSIONS

Ketoconazole reduces the apparent clearance of oral etoposide, does not alter its toxicity profile and does not reduce interpatient pharmacokinetic variability. Other methods to reduce the pharmacokinetic variability of oral etoposide are needed.

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.

A phase I and pharmacokinetic study of irinotecan in patients with hepatic or renal dysfunction or with prior pelvic radiation: CALGB 9863

BACKGROUND

To ascertain if hepatic or renal dysfunction or prior pelvic radiation (XRT) leads to increased toxicity at a given dose of irinotecan and to characterize the pharmacokinetics of irinotecan and its major metabolites in patients with hepatic or renal dysfunction.

PATIENTS AND METHODS

Adults with tumors appropriate for irinotecan therapy and who had abnormal liver or renal function tests or had prior radiation to the pelvis were eligible. Patients were assigned to one of four treatment cohorts: I, aspartate aminotransferase (AST) > or = 3x upper limit of normal and direct bilirubin <1.0 mg/dl; II, direct bilirubin 1.0-7.0 mg/dl; III, creatinine 1.6-5.0 mg/dl with normal liver function; IV, prior pelvic XRT with normal liver and renal function. Starting with reduced doses of either 145 or 225 mg/m(2), irinotecan was administered every 3 weeks to at least three patients within each cohort. Irinotecan and its metabolites in the blood were measured in all patients.

RESULTS

Thirty-five patients were evaluable for toxicity. No dose-limiting toxicity was seen in cohort I, although only three patients were treated and at a dose of 225 mg/m(2). Patients with elevations of direct bilirubin had dose-limiting toxicities, even though the starting dose was 145 mg/m(2). These same patients appeared to have comparable exposure to the active metabolite SN-38 as normal patients treated with full-dose irinotecan. Patients with elevations of creatinine or with prior pelvic radiotherapy did not appear to have increased risk of toxicity at the doses explored in this study.

CONCLUSIONS

Patients with elevated bilirubin treated with irinotecan have an increased risk of toxicity and a dose reduction is recommended. Patients with elevated AST, creatinine or prior pelvic radiation do not appear to have increased sensitivity to irinotecan, but the data are not adequate to support a specific dosing recommendation.

Anaesthetic implications of anticancer chemotherapy

In anaesthetic practice we deal with cancer patients who are scheduled for operations on tumours or other manifestations of malignant disease. Those patients are often debilitated and have significant weight loss accompanied with hypoproteinaemia, anaemia and coagulation disorders. Oncological patients usually present to the anaesthetist before tumour disease surgery, but they are also candidates for elective operations (e.g. hernia repair) and urgent/emergency surgery (e.g. trauma, fractures and ileus). Chemotherapeutic agents given to these patients are potentially noxious, can affect the conduct of anaesthesia and, furthermore, may aggravate the patient's condition. In this review the most commonly used cytostatic drug regimens and their common side-effects are listed. Some preclinical studies on anaesthetic and cytostatic drug metabolism and interactions are emphasized, as well as clinically relevant perioperative alterations that may affect anaesthetic management in cancer patients. An anaesthetist may have to modify a routine anaesthetic regimen in cancer patients especially if anticancer chemotherapeutics were given. Clinically silent toxic drug effects may become apparent during operation, trauma or in the early postoperative course in such patients. Altered reactions to commonly used anaesthetics in patients receiving chemotherapeutics and an impaired stress reaction may occur in such patients. Special attention must be drawn to protection against opportunistic infections.

Pharmacology of anticancer drugs in the elderly population

Modifications to bodily functions and physiology are known to occur with age. These changes can have a considerable impact on the pharmacokinetic processes of absorption, distribution, metabolism and excretion and the pharmacodynamic properties of administered drugs. For many drugs with a high therapeutic index, this will be clinically unimportant, but for anticancer drugs, which usually have a low therapeutic index, these pharmacological changes can lead to dramatic consequences, such as excessive drug concentrations and unacceptable toxicity, or subtherapeutic drug concentrations and ineffective treatment. Despite the increased susceptibility of the elderly to these changes, doses are rarely adapted on the basis of pharmacokinetics and pharmacodynamics, with the exception of changes secondary to altered renal function. Until recently, only a few large prospective randomised trials have provided evidence-based data for dose adaptations in elderly patients. However, with increasing knowledge of the pharmacokinetics of anticancer drugs, advances in the knowledge of pharmacokinetic behaviour with aging, and documented efficacy and toxicity data in the elderly population, it is possible to highlight aspects of prescribing anticancer drugs in the elderly. In general, and for most drugs, age itself is not a contraindication to full-dose chemotherapy. The main limiting factors are comorbidity and poor functional status, which may be present in a significant number of the elderly population. Elderly patients with cancer are part of the daily practice of oncologists, but currently clinicians can often only estimate whether dose modification is advantageous for the elderly. This review attempts to elucidate the factors that can influence the pharmacokinetics of anticancer drugs frequently used in the elderly, and the clinical or biochemical parameters that form the basis for dose adjustments with age.

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.

Comparative pharmacokinetic study of high-dose etoposide and etoposide phosphate in patients with lymphoid malignancy receiving autologous stem cell transplantation

The pharmacokinetics of two etoposide (E) formulations were evaluated in patients with refractory hematologic malignancies receiving high-dose conditioning with autologous stem cell transplantation. Patients were randomized to either E at 800 mg/m(2) (containing polysorbate 80 and polyethylene glycol) or etoposide phosphate (EP) at 910 mg/m(2) on days -7 and -5, prior to melphalan, 80 mg/m(2) on day -5. On day -3, EP was repeated. Plasma E was analyzed after each formulation on days -7 and -5 to compare intrapatient pharmacokinetics. In total, 10 patients were treated: four each with multiple myeloma or Hodgkin's disease and two with non-Hodgkin's lymphoma. Mucositis was the major toxicity with seven patients. EP first produced grade 3 mucositis. There was no procedure-related mortality and eight patients remained alive 1 year post-transplant. Cumulative etoposide exposure (AUC) was slightly greater with EP (P=0.056). Conversely, the volume of distribution was slightly, 33%, larger (P=0.052) and clearance was increased with the E infusion (P=0.14). As none of the differences reached statistical significance, both E formulations appear to be pharmacokinetically equivalent in the high-dose transplant setting. The combination of high-dose EP with melphalan is an active preparative regimen prior to ABMT for hematologic malignancies.

Effects of impaired renal function on the pharmacokinetics and toxicity of i.v. ZD9331, a novel non-polyglutamated thymidylate synthase inhibitor, in adult patients with solid tumors

ZD9331 is a potent thymidylate synthase inhibitor. Renal and hepatic clearances were found to be important routes of elimination. The objectives of this pharmacologic trial were to investigate the effect of renal impairment on the pharmacokinetics of ZD9331, to study the toxicity profile and to document any antitumor effects of ZD9331 when administered i.v. to patients with different degrees of renal impairment. Patients were treated with ZD9331 130 mg/m2 given as an i.v. infusion on day 1 of a 4-week cycle to allow full pharmacokinetic assessment. Subsequent cycles involved the administration of ZD9331 on days 1 and 8, every 3 weeks. Patients were stratified according to their renal function assessed by the creatinine clearance: normal renal function (creatinine clearance > or =60 ml/min), mildly impaired renal function (creatinine clearance > or =40 to <60 ml/min) and moderately impaired renal function (creatinine clearance >25 to <40 ml/min). For pharmacokinetic analysis plasma sampling was performed during the first course and assayed using a validated liquid chromatographic tandem mass spectrometry assay. Twenty-three patients were entered on the study, of whom 21 received 130 mg/m2 ZD9331 in the first treatment cycle. No relationship was seen between renal impairment and plasma clearance nor with the area under the concentration-time curve of free ZD9331. Increasing renal impairment was associated with a greater incidence of myelosuppression. No predictive relationship between the clearance of free ZD9331 and the degree of renal impairment as determined by creatinine clearance could be assessed. However, data from this trial indicate that increased renal impairment may be associated with greater ZD9331-induced toxicity, particularly myelosuppression, although this cannot be attributed to any alteration in the plasma pharmacokinetics of ZD9331. Therefore, it may be necessary to administer a reduced dose of ZD9331 to patients with impaired renal function.

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.

High-performance liquid chromatographic methods for the determination of topoisomerase II inhibitors

Various methods for separating eleven different types of topoisomerase II (TOPO-2) inhibitors, including epipodophyllotoxins, anthracyclines, anthracenediones, anthrapyrazoles, anthracenebishydrazones, indole derivatives, aminoacridines, benzisoquinolinediones, isoflavones, bisdioxopiperazines and thiobarbituric acids, are summarized. Proper sample preparation and storage is critical to the successful analysis of some TOPO-2 inhibitors due to difficulties associated with adsorption, instability and complex biological components. Solid-phase and liquid-liquid extractions are widely used to separate TOPO-2 inhibitors from biological samples, although simple deproteinization followed by direct analysis of the supernatant is preferable to extraction based on its speed and simplicity. High-performance liquid chromatography (HPLC) is the favored method for the bioanalysis of TOPO-2 inhibitors. UV or diode array detection is generally employed for early pharmacokinetic studies, while fluorescence or electrochemical detection is used more frequently for analytes with fluorescent or oxidative-reductive properties. For analyses requiring highly sensitive and/or specific detection, electrospray mass spectrometry (ESI-MS or ESI-MS-MS) provides a suitable alternative. A comprehensive compilation of the HPLC techniques currently used to separate TOPO-2 inhibitors will aid the future development of analytical methods for new TOPO-2 inhibitors.

Population pharmacokinetics and pharmacodynamics of oral etoposide

AIMS

To study the population pharmacokinetics and pharmacodynamics of oral etoposide in patients with solid tumours.

METHODS

A prospective, open label, cross-over, bioavailability study was performed in 50 adult patients with miscellaneous, advanced stage solid tumours, who were receiving oral (100 mg capsules) etoposide for 14 days and i.v. (50 mg) etoposide on day 1 or day 7 in randomised order during the first cycle treatment. Total and unbound etoposide concentration were assayed by h.p.l.c. Population PK parameters estimation was done by using the P-Pharm software (Simed). Haematological toxicity and tumour response were the main pharmacodynamic endpoints.

RESULTS

Mean clearance was 1.14 l h(-1) (CV 25%). Creatinine clearance was the only covariable to significantly reduce clearance variability (residual CV 18%). (CL = 0.74 + 0.0057 CLCR; r(2) = 0.32). Mean bioavailability was 45% (CV 22%) and mean protein binding 91.5% (CV 5%). Exposure to free, pharmacologically active etoposide (free AUC p.o.) was highly variable (mean value 2.8 mg l(-1) h; CV 64%; range 0.4-9.5). It decreased with increased creatinine clearance and increased with age which accounted for 9% of the CV. Mean free AUC p.o. was the best predictor of neutropenia. Free AUC50 (exposure producing a 50% reduction in absolute neutrophil count) was 1.80 mg l(-1) h. In patients with lung cancer, the free AUC p.o. was higher in the two patients with responsive tumour (5.9 mg l(-1) h) than in patients with stable (2.1 mg l-1 h) or progressive disease (2.3 mg l-1 h) (P = 0.01).

CONCLUSIONS

Exposure to free etoposide during prolonged oral treatment is highly variable and is the main determinant of pharmacodynamic effects. The population PK model based on creatinine clearance is poorly predictive of exposure. Therapeutic drug monitoring would be necessary for dose individualization or to study the relationship between exposure and antitumour effect.

Phase I and pharmacokinetic trial of gemcitabine in patients with hepatic or renal dysfunction: Cancer and Leukemia Group B 9565

PURPOSE

To ascertain if hepatic or renal dysfunction leads to increased toxicity at a given dose of gemcitabine and to characterize the pharmacokinetics of gemcitabine and its major metabolite in patients with such dysfunction.

PATIENTS AND METHODS

Adults with tumors appropriate for gemcitabine therapy and who had abnormal liver or renal function tests were eligible. Patients were assigned to one of three treatment cohorts: I-AST level less than or equal to two times normal and bilirubin level less than 1.6 mg/dL; II-bilirubin level 1.6 to 7.0 mg/dL; and III-creatinine level 1.6 to 5.0 mg/dL with normal liver function. Doses were explored in at least three patients within each cohort. Gemcitabine and its metabolite were to be measured in the blood in all patients.

RESULTS

Forty patients were assessable for toxicity. Transient transaminase elevations were observed in many patients but were not dose limiting. Patients with AST elevations tolerated gemcitabine without increased toxicity, but patients with elevated bilirubin levels had significant deterioration in liver function after gemcitabine therapy. Patients with elevated creatinine levels had significant toxicity even at reduced doses of gemcitabine, including two instances of severe skin toxicity. There were no apparent pharmacokinetic differences among the three groups or compared with historical controls.

CONCLUSION

If gemcitabine is used for patients with elevations in AST level, no dose reduction is necessary. Patients with elevated bilirubin levels have an increased risk of hepatic toxicity, and a dose reduction is recommended. Patients with elevated creatinine levels seem to have increased sensitivity to gemcitabine, but the data are not adequate to support a specific dosing recommendation.

Benefits of pharmacological knowledge in the design and monitoring of cancer chemotherapy

Prescribing chemotherapy is a difficult task, because of drug resistance, which prevents all tumors to respond to a given protocol and because of drug toxicity, which is generally unavoidable but which must be limited to acceptable levels. The therapeutic window of anticancer drugs is very narrow and clinicians have to try to optimize the individual doses and schedules of the drugs to be administered. They can rely upon simple anthropometric features, such as body weight or surface area; they can also take into account the physiological status of the patient: age, liver and kidney function, genetic characteristics of drug metabolism, etc. The best way for dose adaptation lies in the establishment of pharmacokinetic/pharmacodynamic relationships, i.e., between the behavior of a drug in the body and its efficacy and toxicity. When it is established that the optimal effect of a drug is related to a given parameter, such as the area under the curve plotting plasma concentration vs. time (AUC), it becomes possible to administer the drug with the dose allowing to obtain the target parameter value. Individual dose adaptation can be achieved thanks to the study of the pharmacokinetics of a test dose preceding that of the therapeutic dose, or by the measure of drug plasma levels, either at steady state during a protracted infusion, or from cycle to cycle during repetitive protocols. Population analysis now allows the adaptation of anticancer drug dosing from a minimum knowledge of individual pharmacokinetic features, together with other characteristics of the patients such as age, gender or physiological functions.

Determination of unbound etoposide concentration in ultrafiltered plasma by high-performance liquid chromatography with fluorimetric detection

Etoposide is a highly protein bound drug, and monitoring the concentration of free drug could help individualize dosage in oncological patients. The cost and difficulty of the standard techniques (equilibration dialysis) has hampered the monitoring of free drugs. We describe a simple HPLC method for the measurement of free etoposide concentration in plasma. Sample preparation involves the ultrafiltration of plasma by a Centrifree device for 30 min at 2000 g and extraction with chloroform. The isocratic separation is performed with a mu Bondapak phenyl analytical column. Fluorimetric detection is used (288-328 nm excitation and emission wavelengths). Linearity of the calibration curve is excellent between 0.05 and 1 microgram/ml. Accuracy and precision are reported at the concentrations 0.06 and 0.4 microgram/ml: within-run accuracy is 10% and 6.2%, respectively; between-run accuracy is < or = 1%; within-run coefficients of variation (C.V.) are 10.6 and 5.0%; between-run C.V. are 11.6 and 6.8% respectively. The range of the assay is 0.05 to 1 microgram/ml. The feasibility of the technique has been tested in 7 patients treated with oral etoposide for hepatocarcinoma (mean protein binding 91%). We found no interference from endogenous substances, co-administered drugs (alizapride, furosemide, ranitidine) and other antineoplastic agents (doxorubicine, idarubicine, vinblastine, vinorelbine).

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.

Therapeutic drug monitoring of etoposide in a 14-day infusion for non-small-cell lung cancer

We investigated whether a constant plasma concentration could be obtained by the individualized administration of low-dose, prolonged-infusional etoposide. Etoposide was infused for 14 days at 40 mg/m2/day initially in patients with inoperable non-small-cell lung cancer. The infusion rate was modified based upon the etoposide concentration at 24 h following the initiation of the infusion (C24) to achieve a target concentration of 1.5 microgram/ml. We postulated that severe toxicities could be avoided by maintaining the steady-state concentration at less than 2 microgram/ml, while antitumor activity could be expected if the steady-state concentration was maintained at more than 1 microgram/ml. In a total of 21 courses in 12 patients, the mean etoposide dose was 35+/-6 mg/m2 daily. The C24 was 1.8+/-0.4 microgram/ml and ranged from 1.1 to 2.9 microgram/ml. Following dose modification, the mean concentration from 96 to 336 h (C mean) was 1.6+/-0.2 microgram/ml and ranged from 1.2 to 2.0 microgram/ml. The toxicities were well-tolerated except for one patient with WHO grade 4 leukopenia and neutropenia who developed infectious complications. There were no treatment-related deaths. Following dose modification, the inter-patient variability was decreased successfully. Although this pharmacologically-guided method needs to be validated using more patients, it could be used for therapeutic drug monitoring.

Phase II study of oral etoposide for patients with advanced breast cancer

BACKGROUND

The objective of this study was to define the activity and toxicity of etoposide for patients with previously treated metastatic breast cancer.

METHODS

Thirty patients with measurable metastatic breast cancer who progressed after prior chemotherapy, hormonal therapy, or both, either as adjuvant therapy or for metastatic disease, were enrolled. There were 26 patients evaluable for response and 30 evaluable for toxicity. Treatment consisted of oral etoposide at a dose of 50 mg/m2/day administered for 21 consecutive days. Doses were modified depending on toxicity. Patients were evaluable for response after at least one cycle of therapy.

RESULTS

One complete response and four partial responses were observed. The overall objective response rate was 19% (5/26). Six patients had stable disease. Toxicity consisted mainly of Grade 4 neutropenia for 24% and Grade 4 thrombocytopenia for 13% of patients. There was one death due to neutropenic sepsis.

CONCLUSION

Oral etoposide is an effective, easily administered outpatient regimen with minimal toxicities. Etoposide is effective for patients with pretreated metastatic breast cancer.

A population model for the leukopenic effect of etoposide

We present a new model-dependent approach to quantify hematologic toxicity in a patient population after anticancer therapy. The population model consists of three submodels that are simultaneously fit to the data: (1) a cubic spline function describing the average response of the population versus time ("structural model"), (2) a covariate model, which relates parameters of the structural model to measured demographic or therapeutic variables that are found to be of predictive value (in this study: white blood cell (WBC) count baseline, drug concentration, serum albumin, and serum bilirubin concentration), and (3) a variance model, which estimates the contribution to the response from random variability between patients and from variability within patients, both between courses and within courses, between days. To demonstrate the approach, previously reported data from 118 courses of etoposide therapy in 71 patients with cancer were used to model the decrease in WBC count after 3-day continuous infusions of drug. The estimated typical response profile is characterized by (1) a lag-time of 4 1/2 days before any WBC count decline is observed, (2) a duration of time below baseline of 22 days, and (3) half-maximal effect (i.e., decrease to 50% of baseline WBC count) after exposure to C50 = 3 mg/L etoposide (mean) over 3 days. Lower serum albumin concentrations, higher bilirubin concentrations, or both are associated with greater effects at a given etoposide exposure. Large variability in the estimated response was found between individuals and within individuals, between courses. The total variabilities (SD) in lag-time, duration of the decrease, and C50 were 1 day, 6 days, and 1.8 mg/L, respectively. The population model can also be used to predict the consequence of as-yet untested therapy and sampling strategies, as well as to relate acceptable risks of toxicity to target drug exposure.

Individual dose adaptation of anticancer drugs

The dose of anticancer drugs is currently adjusted to the patient body surface area, although patients have different abilities to clear anticancer drugs. The dose adjustment to physiological functions permits major toxic accidents to be avoided. The adjustment to tumour drug content is considered, but for ethical or technical reasons, it cannot be used routinely The best criterion for the dose adjustment seems to be drug plasma concentration. The relationship between plasma concentration and efficacy may not be excellent, since it depends on the presence of resistant cells and on the blood flow through the tumour. A relationship between plasma concentration and/or the area under the curve (AUC) with toxicity has been reported with all major anticancer drugs. Different methods of dose adjustment to the drug plasma concentration are reported. In conclusion, dose adjustment to the drug plasma concentration or to the AUC can improve the chemotherapy efficacy, while reducing toxicity.

Etoposide dosage and pharmacodynamics

Etoposide is a schedule-dependent cytotoxic drug with high single agent activity in small-cell lung cancer and lymphoma. Despite its clear dose-dependent myelosuppressive activity, dose-dependent evidence of its anti-tumour activity is harder to demonstrate. A number of reports have correlated haematological toxicity with pharmacokinetic and physiological parameters, which explains some of the variability in dynamic effects that exists between patients. Recent reports have also suggested that anti-tumour response may be related to plasma etoposide concentration. In our own studies we have investigated factors that influence the pharmacodynamic effects of etoposide, principally with regard to haematological toxicity, and these studies have highlighted a number of patient groups who are at risk. Impaired renal function causes a reduction in clearance of etoposide, resulting in increased systemic exposure and more profound myelotoxicity. A 30% dose reduction in this group is recommended to normalise the area under the plasma concentration-time curve (AUC). Patients with low serum albumin concentrations (< 35 g/l) also showed significantly worse haematological toxicity, but with no apparent change in total drug pharmacokinetics. There was, however, an increase in the free drug fraction in this group due to decreased protein binding, such that the free drug AUC was similar to that found in patients with renal dysfunction. This would also indicate that a dose reduction of around 30%-40% is required in this patient group. Patients with normal albumin levels but liver enzyme values (aspartate transaminase or gamma-glutamyl transpeptidase) more than 3 times the upper limit of normal also had a less marked but significant increase in neutropenia. In patients with normal organ function, age was the only significant factor in predicting the degree of leukopenia/neutropenia, and increasing age was also associated with decreasing drug clearance and an increase in drug AUC. A small dose reduction and/or careful monitoring is required in this patient group. Further studies are required to elucidate further the relationship between the pharmacokinetics of etoposide and its pharmacodynamics, particularly with regard to anti-tumor activity, and to determine the role of individualised therapy, based on a pharmacokinetic parameter, in reducing the dynamic variability and optimising the use of this drug.

Effect of gastrectomy on the pharmacokinetics of tegafur, uracil, and 5-fluorouracil after oral administration of a 1:4 tegafur and uracil combination

The effects of gastrectomy on the pharmacokinetics of UFT, a combined oral preparation of 1-(2-tetrahydrofuryl)-5-fluorouracil (tegafur) and uracil at a molar ratio of 1:4, were examined in 26 patients with macroscopic Stage I gastric cancer. In all, 200 mg UFT (in terms of tegafur) was given to 17 patients who underwent partial gastrectomy (9 cases of Billroth I reconstruction, 8 cases of Billroth II reconstruction) and to 9 patients who underwent total gastrectomy with modified Roux-en-Y reconstruction. Before the operation, the area under the curve (AUC) for tegafur, uracil, and 5-fluorouracil (5-FU) was 79.28 +/- 26.88, 4.41 +/- 1.78, and 0.51 +/- 0.20 micrograms h ml-1, respectively. Partial (Billroth I and II) and total gastrectomy did not alter the AUC of tegafur, and partial gastrectomy using the Billroth I and II methods decreased the AUCs of uracil and 5-FU during the first 2 weeks postoperation. However, plasma levels of uracil and 5-FU reverted to preoperative values at 3 months postsurgery. Our findings show that when UFT is prescribed for patients treated in the early postoperative period following partial gastrectomy for cancer, dose increases and the timing of administration should be given close attention.

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.

Clinical trials of modulation of multidrug resistance. Pharmacokinetic and pharmacodynamic considerations

A growing body of evidence indicates that expression of the mdr1 gene, which encodes the multidrug transporter, P-glycoprotein, contributes to chemotherapeutic resistance of human cancers. Expression of this protein in normal tissues such as the biliary tract, intestines, and renal tubules suggests a role in the excretion of toxins. Modulation of P-glycoprotein function in normal tissues may lead to decreased excretion of drugs and enhanced toxicities. A clinical trial of etoposide with escalating doses of cyclosporine (CsA) as a modulator of multidrug resistance was performed. CsA was delivered as a 2-hour loading dose followed by a 60-hour intravenous infusion, together with etoposide administered as a short infusion daily for 3 days. Patients received one or more courses of etoposide alone before the combined therapy to establish their clinical resistance to etoposide and to study etoposide pharmacokinetics without and then with CsA. Plasma and urinary etoposide was measured by high-performance liquid chromatography and plasma CsA by a nonspecific immunoassay. Conclusions from the initial phase I trial with the use of CsA as a modulator of etoposide are: (1) Serum CsA steady-state levels of up to 4800 ng/ml (4 microM) could be achieved with acceptable toxicity. (2) Toxicities caused by the combined treatment included increased nausea and vomiting, increased myelosuppression, and hyperbilirubinemia, consistent with modulation of P-glycoprotein function in the blood-brain barrier, hematopoietic stem cell, and biliary tract. Renal toxicity was uncommon, but severe in two patients with steady-state plasma CsA levels above 6000 ng/ml. (3) CsA administration had a marked effect on the pharmacokinetics of etoposide, with a doubling of the area under the concentration-time curve as a result of both decreased renal and nonrenal clearance, necessitating a 50% dose reduction in patients with normal renal function and hepatic function. (4) The recommended dose of CsA is a 6-7 mg/kg loading dose administered as a 2-hour intravenous infusion followed by a continuous infusion of 18-21 mg/kg/day for 60 hours with adjustments in the infusion rate to maintain steady-state serum levels of 3000-4800 ng/ml (2.5-4.0 M). We are performing additional phase I trials combining CsA with single-agent doxorubicin and taxol, and the CsA analog PSC-833 with various multidrug-resistant-related cytotoxins.

In vivo accumulation of etoposide in peripheral leukemic cells in patients treated for acute myeloblastic leukemia; relation to plasma concentrations and protein binding

Since etoposide interacts with the nuclear enzyme topoisomerase II, the drug concentrations in the malignant cells during chemotherapy may have clinical correlates. Plasma protein binding of etoposide is extensive (94%) and alterations of the non-proteinbound fraction affect pharmacokinetic behavior of the drug. The pharmacokinetics of etoposide was therefore studied in plasma, total and non-proteinbound concentrations, and in leukemic cells isolated from peripheral blood samples from 22 patients after the first dose of the induction treatment for acute myelocytic leukemia. Fourteen patients received 100 mg/m2 and eight patients 200 mg/m2 as a 1 h infusion. The mean area under the concentration versus time curve AUC(0-infinity) in plasma was at the lower dose level 78.4 +/- 29.1 (mean +/- S.D.) micrograms/ml x h and 201.0 +/- 56.5 micrograms/ml x h at the higher dose level. The fraction of non-proteinbound etoposide in plasma was 5.2 +/- 3.4 and 5.4 +/- 2.1% in the two treatment groups. AUC(0-16h) in leukemic cells was 8.4 +/- 8.7 and 22.4 +/- 12.1 micrograms/ml x h at the two dose levels, respectively. The cellular etoposide concentration was 12.1 +/- 7.9 and 14.7 +/- 5.1% of the plasma concentration at the end of the infusion. The interpatient variability in cellular drug levels was considerable and exceeded the variability in plasma concentrations. Cellular accumulation of etoposide could be important for treatment outcome.

Disposition of total and unbound etoposide following high-dose therapy

Total and unbound etoposide pharmacokinetics were studied in 16 adult patients (median age, 34 years; range, 18-61 years) undergoing autologous bone marrow transplantation for advanced lymphoma after receiving high-dose etoposide (35-60 mg/kg) as a single intravenous infusion. Pretreatment values for mean serum albumin and total bilirubin were 3.0 +/- 0.4 g/dl and 0.5 +/- 0.4 mg/dl, respectively. Etoposide plasma concentrations and protein binding (%unbound) were determined by high-performance liquid chromatography (HPLC) and equilibrium dialysis, respectively. Pharmacokinetic parameters for unbound and total etoposide were calculated by nonlinear regression analysis using a two-compartment model. The mean (+/- SD) parameters for total etoposide included: clearance (CL), 31.8 +/- 17.7 ml min-1 m-2; volume of distribution (Vss), 11.5 +/- 5.9 l/m2, and terminal half-life (t1/2 beta), 7.2 +/- 3.7 h. Mean unbound CL was 209.6 +/- 62.7 ml min-1 m-2 and %unbound was 16% +/- 5%. The mean etoposide %unbound was inversely related to serum albumin (r2 = 0.45, P = 0.0043). The mean %unbound at the end of the etoposide infusion was higher than that at the lowest measured concentration (21% vs 13%, respectively; P = 0.017), suggesting that concentration-dependent binding may occur after high etoposide doses. The median total CL was higher in patients with serum albumin concentrations of < or = 3.0 g/dl than in those with levels of > 3.0 g/dl (34.6 vs 23.5 ml min-1 m-2, P = 0.05). Total CL was directly related to %unbound (r2 = 0.61, P = 0.0004). Unbound CL was unrelated to either serum albumin or %unbound. These results demonstrate that hypoalbuminemia is independently associated with an increased etoposide %unbound and rapid total CL after the administration of high-dose etoposide. Unbound CL in hypoalbuminemic patients is unchanged in the presence of normal total bilirubin values.

Factors affecting in vitro protein binding of etoposide in humans

Clinical studies have demonstrated that the plasma protein binding of etoposide, a widely used anticancer drug, is extensive (approximately 94%), highly variable among patients (10-fold range), and significantly related to serum albumin and total bilirubin concentration. The present study was designed to more thoroughly evaluate factors likely to affect etoposide protein binding under controlled in vitro conditions where single variables could be changed. Protein binding was determined using an equilibrium dialysis method with tritiated etoposide. The binding of etoposide was similar in serum or plasma, and heparin had no effect on binding. Etoposide binding decreased with increased pH, but no clinically significant difference was noted within the range of physiologic pH. Etoposide binding evaluated in single-source donor plasma was concentration-dependent over a concentration range of 1 to 250 micrograms/mL. Etoposide binding parameters determined in normal human plasma were characterized by a single class of binding sites of moderate affinity (K = 2.88 +/- 0.47 x 10(4)) and high capacity (nP = 5.07 +/- 0.5 x 10(-4); where n is the number of binding sites). The etoposide binding ratio was significantly correlated with albumin concentration (r2 = 99%, p less than 0.05). The characteristics of etoposide binding in a 4.0-g/dL solution of human serum albumin (K = 3.56 +/- 1.22 x 10(4) and nP = 5.58 +/- 0.16 x 10(-4)) suggest that the single class of binding sites is on albumin. Bilirubin caused a significant decrease in K, consistent with competitive binding, but only at higher bilirubin concentrations.(ABSTRACT TRUNCATED AT 250 WORDS)

Pharmacodynamics of three daily infusions of etoposide in patients with extensive-stage small-cell lung cancer

The objectives of this study were to define the pharmacodynamics of etoposide and to develop potentially useful models (1) to estimate the plasma clearance using a limited number of samples and (2) to describe the relationship between clearance and the dose-limiting toxicity. A total of 17 patients with extensive-stage small-cell lung cancer were treated with 150 mg/m2 etoposide daily for 3 consecutive days and with 100 mg/m2 cisplatin on day 3 only. Both drugs were given intravenously over 1 h. Treatment was repeated every 21 days for up to six courses. All patients were newly diagnosed (no previous chemotherapy or irradiation) and had a performance status of 0-2. Six patients achieved a complete response as confirmed by repeat bronchoscopy and five patients showed a partial response, for an overall objective response rate of 65% (95% confidence interval, 38%-87%). The median survival was 8 months (range, 1-24+ months). The dose-limiting toxicity was neutropenia. Etoposide pharmacokinetics were measured during the first course and determinations were repeated during courses 3 or 4 and 6. Complete blood counts were obtained weekly. Correlations for etoposide clearance and hematologic toxicities were evaluated for 17 initial courses and for an overall number of 33 courses. Pharmacodynamic correlations were significant for graded hematologic toxicities, as well as nadirs of leukocytes, neutrophils, and platelets for the initial courses and for all courses. To reduce the requirement for numerous blood samples, a limited sampling model was developed to estimate the area under the concentration versus time curve (AUC) with the following equation: AUC = 15.45 + 3.86 x C2 + 7.10 x C4, where C2 and C4 represent the etoposide concentrations at 2 and 4 h, respectively. The total plasma clearance was calculated as the dose divided by the AUC; correlations with toxicity were better for clearance expressed in milliliters per minute than for that expressed in milliliters per minute per square meter of body surface area. The absolute neutrophil count at the nadir (ANCn) can be estimated by the following pharmacodynamic model, which is based on 33 courses: ANCn = -0.399 + 0.024 x Ecl, where Ecl represents the etoposide clearance expressed in milliliters per minute. Further studies are necessary to validate both models prospectively.