Adaptive control of etoposide administration: impact of interpatient pharmacodynamic variability

[Anaemia: What is its relationship with the frailty syndrome in elderly patients?]

Anaemia is often unexpectedly found, or in a context of investigations into a chest pain, dyspnoea, or weakness. This disorder can be considered an indicator of health status in elderly patients, and has been related to the frailty syndrome. A systematic review was conducted on the studies published in PubMed and Google Scholar databases in the period from January 1999 to May 2019. The search was limited to those studies published regarding anaemia and its relationship to the frailty syndrome. Anaemia seems to be part of the immunosenescence process that can explain frailty syndrome in association with other metabolism, endocrine, and inflammatory disorders. It was unable to be determined if anaemia is responsible for frailty or a result of it.

Anemia, Cancer, and Aging

BACKGROUND

Anemia is an issue of concern in the management of older patients with cancer. In this age group, the incidence and prevalence of both cancer and anemia increase with age.

METHODS

The clinical consequences and the management of anemia, a common comorbid condition in older patients with cancer, are explored.

RESULTS

Common causes of chronic anemia include iron deficiency and anemia of chronic disease. The prevalence of vitamin B12 deficiency due to reduced absorption of food-bound vitamin B12 also increases with aging. Although in many cases the cause of anemia is not found, a primary deficiency of erythropoietin may be at fault in at least some of these cases since the response of erythropoietin to anemia may decrease in individuals over age 70.

CONCLUSIONS

Anemia should not necessarily be ascribed to cancer or aging. The causes of anemia should be pursued and reversed, and hemoglobin levels should be maintained at a minimum of 12 g/dL in cancer patients undergoing chemotherapy who are responsive to erythropoietin. The reversal of anemia may offset or delay the accumulation of catabolic cytokines that may be responsible for functional decline in aging individuals.

Pharmacology of Chemotherapy in the Older Cancer Patient

Background

The incidence of cancer among the elderly population is increasing. The aging process can deplete functional reserve of many organ systems and thus affects the treatment goals for this age-group.

Methods

The pharmacologic consequences of the aging process on elderly cancer patients are reviewed, and guidelines are suggested for assessing and treating this patient population with antitumor drugs.

Results

Individualized management of the older cancer patient reflects the results of a comprehensive geriatric assessment. Factors that affect treatment decisions include estimates of the extent of treatment toxicity, the impact of treatment on quality of life, estimates of life expectancy, and the influence of age on pharmacokinetic parameters.

Conclusions

Management of older patients with cancer includes individual assessments that consider the effects of aging on the pharmacodynamics, therapies, and complications of treatment for this population. Treatment can be made safer and more effective by adjusting chemotherapy dosage, maintaining hemoglobin levels, and using hemopoietic growth factors when appropriate.

Supportive care considerations for older adults with cancer

The treatment of cancer presents specific concerns that are unique to the growing demographic of elderly patients. Because the incidence of cancer is strongly correlated with aging, the expansion of supportive care and other age-appropriate therapies will be of great importance as the population of elderly patients with cancer increases in the coming years. Elderly patients are especially likely to experience febrile neutropenia, complications from chemotherapy-induced nausea, anemia, osteoporosis (especially in patients diagnosed with breast or prostate cancer), depression, insomnia, and fatigue. These issues are often complicated by other chronic conditions related to age, such as diabetes and cardiac disease. For many patients, symptoms may be addressed both through lifestyle management and pharmaceutical approaches. Therefore, the key to improving quality of life for the elderly patient with cancer is an awareness of their specific needs and a familiarity with emergent treatment options.

Anemia, fatigue and aging

Aging is associated with increased incidence and prevalence of both cancer and anemia. Cancer and aging may conspire in making anemia more frequent and more severe. This article reviews the causes and the consequences of anemia in the older individual. The most common causes include chronic inflammation that is a typical manifestation of aging, iron deficiency that may be due to chronic hemorrhage, malabsorption and Helicobacter pylori infection, cobalamin deficiency from malabsorption and renal insufficiency. Other causes of anemia whose prevalence is not well established include myelodysplasia, copper deficiency, hypothyroidism, and sarcopenia. Anemia is associated with increased risk of mortality, functional dependence, dementia, falls, and chemotherapy-related toxicity. When correcting the anemia of older cancer patients one should remember that the erythropoietic stimulating agents (ESA) may stimulate cancer growth and cause thrombosis. These products may be safe when given exclusively to patients receiving chemotherapy and when the hemoglobin levels are maintained below 12 g/dL.

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.

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.

Anemia in the elderly—Clinical findings and impact on health

Anemia is common in older people and it becomes more so with advancing decades. Because the older population is increasing, the prevalence of anemia and consequently its impact on health and healthcare expenditure is expected to rise. Although the causes and consequences of anemia have not been fully elucidated and its etiology is occasionally elusive, clinical evidence has indicated that anemia itself is a cause of morbidity and it can complicate other health conditions. The clinical approach to anemia is evolving. In the past, anemia was mainly seen as a sign of underlying disease; today, anemia is considered to be a cause of severe deterioration of quality of life, morbidity, and decline in physical function, and a risk factor for death. A better understanding of anemia in the elderly will lead to improved treatment strategies, including the more judicious use of transfusion and appropriate use of erythropoietic agents.

Individualised Cancer Chemotherapy: Strategies and Performance of Prospective Studies on Therapeutic Drug Monitoring with Dose Adaptation

Therapeutic drug monitoring (TDM) is increasingly used in clinical practice for the optimisation of drug treatment. Although pharmacokinetic variability is an established factor involved in the variation of therapeutic outcome of many chemotherapeutic agents, the use of TDM in the field of oncology has been limited thus far. An important reason for this is that a therapeutic index for most anticancer agents has not been established; however, in the last 20 years, relationships between plasma drug concentrations and clinical outcome have been defined for various chemotherapeutic agents. Several attempts have been made to use these relationships for optimising the administration of chemotherapeutics by applying pharmacokinetically guided dosage. These prospective studies, individualising chemotherapy dose during therapy based on measured drug concentrations, are discussed in this review. We focus on the way a target value is defined, the methodologies used for dose adaptation and the way the performance of the dose-adaptation approach is evaluated. Furthermore, attention is paid to the results of the studies and the applicability of the strategies in clinical practice. It can be concluded that TDM may contribute to improving cancer chemotherapy in terms of patient outcome and survival and should therefore be further investigated.

Supportive care of the older cancer patient

Aging is associated with decreased functional reserve of multiple organ systems and with changes in the pharmacokinetics and pharmacodinamics of drugs. Older individuals express enhanced susceptibility to the complications of cytotoxic chemotherapy, especially to myleotoxicity, mucositis, cardiotoxicity and neurotoxicity. The management of older individuals with chemotherapy involves then prevention of these complications. General precautions include proper patient selection, based on the comprehensive geriatric assessment (CGA), dose adjustment for agents that are renally excreted to the patient creatinine clearance and maintenance of hemoglobin levels > or =12 g/dl. Filgrastim and pegfilgrastim proved effective in reducing by 50-75% the risk of neutropenic fever in older individuals treated with CHOP and CHOP-like chemotherapy and should be used for the prophilaxis of infections. When feasible, the oral agent capecitabine, should be used in lieu of intravenous fluorinated pyrimidines, to prevent mucositis. In patients at risk of cardiomyopathy from anthracyclines, dexrazoxane or liposomal compounds may be indicated. When toxicity is properly prevented, cytotoxic chemotherapy may be as effective in older individuals as it is in the younger ones.

Complications of cytotoxic chemotherapy in older patients: focus on myelotoxicity in lymphomas

The management of the older lymphoma patient with cytotoxic chemotherapy requires knowledge of the pharmacologic effects of age and awareness of the diversity of the older population. The most obvious reason for attenuation of treatment intensity in the elderly is the possibility of a decline in hemopoietic reserve. The research of specific therapeutic protocols is needed to cure the elderly lymphoma patients reducing the risk of important toxic effects.

Mechanistic models for myelosuppression

As myelosuppression is the dose-limiting toxicity for most chemotherapeutic drugs, modelers attempt to find relationships between drug and toxicity to optimize treatment. Mechanistic models, i.e. models based on physiology and pharmacology, are preferable over empirical models, as prior information can be utilized and as they generally are more reliable for extrapolations. To account for different dosing-regimens and possible schedule-dependent effects, the whole concentration-time profile should be used as input into the pharmacokinetic-pharmacodynamic model. It is also of importance to model the whole time course of myelosuppression to be able to predict both the degree and duration of toxicity as well as consecutive courses of therapy. A handful of (semi)-mechanistic pharmacokinetic-pharmacodynamic models with the above properties have been developed and are reviewed. Ideally, a model of myelosuppression should separate drug-specific parameters from system related parameters to be applicable across drugs and useful under different clinical settings. Introduction of mechanistic models of myelosuppression in the design and evaluation of clinical trials can guide in the decision of optimal sampling times, contribute to knowledge of optimal doses and treatment regimens at an earlier time point and identify sub-groups of patients at a high risk of myelosuppression.

Model of chemotherapy-induced myelosuppression with parameter consistency across drugs

PURPOSE

To develop a semimechanistic pharmacokinetic-pharmacodynamic model describing chemotherapy-induced myelosuppression through drug-specific parameters and system-related parameters, which are common to all drugs.

PATIENTS AND METHODS

Patient leukocyte and neutrophil data after administration of docetaxel, paclitaxel, and etoposide were used to develop the model, which was also applied to myelosuppression data from 2'-deoxy-2'-methylidenecytidine (DMDC), irinotecan (CPT-11), and vinflunine administrations. The model consisted of a proliferating compartment that was sensitive to drugs, three transit compartments that represented maturation, and a compartment of circulating blood cells. Three system-related parameters were estimated: baseline, mean transit time, and a feedback parameter. Drug concentration-time profiles affected the proliferation of sensitive cells by either an inhibitory linear model or an inhibitory E(max) model. To evaluate the model, system-related parameters were fixed to the same values for all drugs, which were based on the results from the estimations, and only drug-specific parameters were estimated. All modeling was performed using NONMEM software.

RESULTS

For all investigated drugs, the model successfully described myelosuppression. Consecutive courses and different schedules of administration were also well characterized. Similar system-related parameter estimates were obtained for the different drugs and also for leukocytes compared with neutrophils. In addition, when system-related parameters were fixed, the model well characterized chemotherapy-induced myelosuppression for the different drugs.

CONCLUSION

This model predicted myelosuppression after administration of one of several different chemotherapeutic drugs. In addition, with fixed system-related parameters to proposed values, and only drug-related parameters estimated, myelosuppression can be predicted. We propose that this model can be a useful tool in the development of anticancer drugs and therapies.

Pharmacokinetic interactions of cyclosporine with etoposide and mitoxantrone in children with acute myeloid leukemia

The purpose of this study was to assess the effect of the multidrug resistance modulator cyclosporine (CsA) on the pharmacokinetics of etoposide and mitoxantrone in children with de novo acute myeloid leukemia (AML). Serial blood samples for pharmacokinetic studies were obtained in 38 children over a 24-h period following cytotoxin treatment with or without CsA on days 1 and 4. Drug concentrations were quantitated using validated HPLC methods, and pharmacokinetic parameters were determined using compartmental modeling with an iterative two-stage approach, implemented on ADAPT II software. Etoposide displayed a greater degree of interindividual variability in clearance and systemic exposure than mitoxantrone. With CsA treatment, etoposide and mitoxantrone mean clearance declined by 71% and 42%, respectively. These effects on clearance, in combination with the empiric 40% dose reduction for either cytotoxin, resulted in a 47% and 12% increases in the mean AUC for etoposide and mitoxantrone, respectively. There were no differences in the rates of stomatitis or infection between the two groups. CsA treatment resulted in an increased incidence of hyperbilrubinemia, which rapidly reversed upon conclusion of drug therapy. The variability observed in clearance, combined with the empiric 40% dose reduction of the cytotoxins, resulted in statistically similar systemic exposure and similar toxicity.

Treatment considerations for the elderly person with cancer

In an aging population, the number of patients with cancer continues to rise. Little research has focused on the treatment of cancer in the elderly. Therefore, the treatment for various cancers differs across the healthcare system. A uniform approach in assessing the elderly person with cancer is lacking. This article describes two case studies in the elderly population, focusing on two common cancers: acute myelogenous leukemia and breast cancer. Common side effects of treatment and determinants of treatment options are discussed. It is important that the elderly receive appropriate screening, early detection, treatment, and management of comorbidities.

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.

Hematopoietic growth factors in the older cancer patient

Aging is associated with a progressive decline in the functional reserve of multiple organ systems, which may lead to enhanced susceptibility to stress such as that caused by cancer chemotherapy. Myelodepression is the most common and the most commonly fatal complication of antineoplastic drug therapy and may represent a serious hindrance to the management of cancer in older individuals. This is already a common and pervasive problem and promises to become more so. Currently 60% of all neoplasms occur in persons aged 65 years and older, and this percentage is expected to increase as the population ages. This well-known phenomenon, sometimes referred to as squaring or the age pyramid, is caused by the combination of an increasing life expectancy and a decreasing birth rate. This article explores the use of hematopoietic growth factors in the older cancer patient after reviewing the influence of age on hemopoiesis and chemotherapy-related complications. The issue is examined in terms of effectiveness and cost. An outline of the assessment of the older cancer patient is provided at the end of the chapter as a frame of reference for clinical decisions.

Body surface area as a determinant of pharmacokinetics and drug dosing

Body surface area (BSA) was introduced into medical oncology in order to derive a safe starting dose for phase I studies of anticancer drugs from preclinical animal toxicology data. It is not clear however, as to why dosing by BSA was extended to the routine dosing of antineoplastic agents. Several formulas exist to estimate BSA, but the formula derived by DuBois and DuBois is the one used in adult medical oncology. This formula was derived based on data from only nine patients; subsequent attempts to validate the formula have found the DuBois formula to either over or underestimate the actual determined BSA. While cardiac output does correlate with BSA, the relationship between BSA and other physiologic measures relevant for drug metabolism and disposition, such as, renal and hepatic function, is weak or nonexistent. Further only epirubicin, etoposide, and carboplatin have been studied to determine if dosing by BSA would reduce interpatient variability, and none of these drugs were found to have significant relationships between their pharmacokinetics and BSA. Future clinical trials of new agents should not presume that dosing based on BSA reduces interpatient variability. Studies should examine the role, if any, BSA has in dosing new chemotherapeutic agents in initial phase I studies.

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

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

Pharmacokinetically guided administration of chemotherapeutic agents

The current practice for the dose calculation of most anticancer agents is based on body surface area in m2, although lower interpatient variation in pharmacokinetic parameters has been reported with pharmacokinetically guided administration. As chemotherapeutic agents have a narrow therapeutic window, pharmacokinetically guided administration may lead to less toxicity and higher efficacy than administration on the basis of body surface area. Pharmacokinetically guided administration, using parameters such as area under the plasma concentration-time curve (AUC), steady-state plasma drug concentration and drug exposure time above a certain plasma concentration, has been studied for many antineoplastic agents. Assessment of pharmacokinetic profiles allows the characterisation of relationships between pharmacokinetic parameters and efficacy and toxicity. AUC appears to be more closely correlated with pharmacodynamics than does the dose per unit of body surface area. In particular, the AUC-guided administration of carboplatin has been extensively studied, based on the close relationship between the renal clearance of the drug and glomerular filtration rate. Several formulae and limited sampling models have been derived to predict the AUC of carboplatin. The relationship between AUC and pharmacodynamics has also been studied for other anticancer agents, for example fluorouracil, topotecan, etoposide, cisplatin and busulfan, but all less extensively than for carboplatin. The pharmacokinetically guided administration of these agents needs to be investigated further before the use of alternative administration formulae can become standard clinical practice. Prospective studies of pharmacokinetically guided versus surface area-based administration should be performed to validate pharmacokinetic-pharmacodynamic relationships and to facilitate optimal dosage of anticancer agents in the clinic.

Hemopoietic reserve in the older cancer patient: clinical and economic considerations

BACKGROUND

Older individuals are at increased risk for myelosuppression, the most common complication of cytotoxic chemotherapy. Causes include reduction in hemopoietic stem cell reserve, increased prevalence of chronic diseases, and increased prevalence of anemia. Anemia is an independent risk factor for myelotoxicity, in part because it decreases the volume of distribution of anthracyclines, epipodophyllotoxins, and taxanes and increases the circulating concentration of free drugs.

METHODS

The authors review the effects of aging on the hemopoietic system and the consequences of reduced hemopoietic reserve on the safety and cost of chemotherapy.

RESULTS

While it is unclear whether the responsiveness of hemopoietic progenitors to physiologic amounts of growth factors is preserved in older individuals, pharmacological doses of these factors stimulate hemopoiesis and mitigate myelosuppression. It is recommended that patients aged 70 and older receiving combination chemotherapy of dose-intensity comparable to CHOP be routinely treated with myelopoietic growth factor. The hemoglobin levels of these patients should be maintained at approximately 12 g/dL with erythropoietin. This treatment may prevent costly complications such as neutropenic infections and functional dependence.

CONCLUSIONS

Alternative approaches to the prevention of hemopoietic complications may include more conservative use of growth factors (later initiation of treatment and earlier termination), prophylactic antibiotics in patients at risk for prolonged neutropenia, and biological treatment. Dose-reduction of chemotherapy may lead to inferior outcomes and is not recommended for patients with good functional status.

Geriatric oncology: challenges for the new century

The management of cancer in the older aged person represents one of the major immediate challenges of medicine. The response to this challenge involves answers to the following questions: I. Who is old? Currently. 70 years of age may he considered the lower limit of senescence because the majority of age-related changes occur after this age. Individual estimates of life expectancy and functional reserve may be obtained by a comprehensive and time-consuming multidimensional geriatric assessment. The current instrument may be fine-tuned and new instruments, including laboratory tests of ageing. may be developed. 2. Why do older persons develop more cancer? It is clear that ageing tissues are more susceptible to late-stage carcinogen. Older persons may represent a natural monitor system for new environmental carcinogens, and may also represent a fruitful ground to study the late stages of carcinogenesis. 3. Is cancer different in younger and older persons? Clearly. the behaviour of some tumors. including acute myeloid leukaemia, non-Hodgkin's lymphoma and breast cancer change with the age of the patient. The mechanisms of these changes that may involve both the tumour cell and the tumour host are poorly understood. 4. Can cancer he prevented in older individuals? Chemoprevention offers a new horizon of possibilities for cancer prevention: older persons may benefit most from chemoprevention due to increased susceptibility to environmental carcinogens. Screening tests may become more accurate in older individuals due to increased prevalence of cancer. hut may he less beneficial due to more limited patient life expectancy. 5. Do older persons benefit from cytotoxic treatment? The answer to this question partly stands on proper patient selection. partly on the development of safer forms of cancer treatment and prudent use of antidotes to chemotherapy toxicity. 6. What is the cost of treating older cancer patients? The treatment of older patients is generally more costly. This cost should be assessed against the cost of not treating cancer and promoting functional dependence. which by itself is extremely costly. 7. What are the endpoints of clinical trials in older cancer patients? With more limited life expectancy. the effect of treatment on quality of life is paramount. Reliable assessment of quality of life is essential for interpreting clinical trials in older individuals. 2000 Elsevier Science Ltd. All rights reserved.

Management of cancer in the older person: a practical approach

The management of cancer in the older aged person is an increasingly common problem. The questions arising from this problem are: Is the patient going to die with cancer or of cancer? Is the patient able to tolerate the stress of antineoplastic therapy? Is the treatment producing more benefits than harm? This article explores a practical, albeit evolving, approach to these questions including a multidimensional assessment of the older person and simple pharmacologic interventions that may ameliorate the toxicity of antineoplastic agents. Age may be construed as a progressive loss of stress tolerance, due to decline in functional reserve of multiple organ systems, high prevalence of comorbid conditions, limited socioeconomic support, reduced cognition, and higher prevalence of depression. Aging is highly individualized: chronologic age may not reflect the functional reserve and life expectancy of an individual. A comprehensive geriatric assessment (CGA) best accounts for the diversities in the geriatric population. The advantages of the CGA include:Recognition of potentially treatable conditions such as depression or malnutrition, that may lessen the tolerance of cancer treatment and be reversed with proper intervention; Assessment of individual functional reserve; Gross estimate of individual life expectancy; and Adoption of a common language to classify older cancer patients. The CGA allows the practitioner to recognize at least three stages of aging:People who are functionally independent and without comorbidity, who are candidates for any form of standard cancer treatment, with the possible exception of bone marrow transplant. People who are frail (dependence in one or more activities of daily living, three or more comorbid conditions, one or more geriatric syndromes), who are a candidate only for palliative treatment; and People in between, who may benefit from some special pharmacological approach, such as reduction in the initial dose of chemotherapy with subsequent does escalations. The pharmacological changes of age include decreased renal excretion of drugs and increased susceptibility to myelosuppression, mucositis, cardiotoxicity and neurotoxicity. Based on these findings, the proposal was made that all persons aged 70 and older, treated with cytotoxic chemotherapy of dose intensity comparable to CHOP, receive prophylactic growth factor treatment, and that the hemoglobin of these patients be maintained >/=12 gm/dl.

Optimizing drug regimens in cancer chemotherapy by an efficacy-toxicity mathematical model

In cancer chemotherapy, it is important to design treatment strategies that ensure a desired rate of tumor cell kill without unacceptable toxicity. To optimize treatment, we used a mathematical model describing the pharmacokinetics of anticancer drugs, antitumor efficacy, and drug toxicity. This model was associated with constraints on the allowed plasma concentrations, drug exposure, and leukopenia. Given a schedule of drug administrations, the mathematical model optimized the drug doses that can minimize the tumor burden while limiting toxicity at the level of the white blood cells. The main result is that the optimal drug administration is an initial high-dose chemotherapy up to saturation of constraints associated with normal cell toxicity and a maintenance continuous infusion at a moderate rate. Data related to etoposide investigations were used in a feasibility study. Simulations with the optimized protocol showed better performances than usual clinical protocols. Model-based optimal drug doses provide for greater cytoreduction, while limiting the risk of unacceptable toxicity.

Adaptive control methods for the dose individualisation of anticancer agents

Numerous studies have found a clear relationship between systemic exposure and the toxicity or (more rarely) the efficacy of anticancer agents. Moreover, the clearance of most of these drugs differs widely between patients. These findings, combined with the narrow therapeutic index of anticancer drugs, suggest that patient outcome would be improved if doses were individualised to achieve a target systemic exposure. Bayesian maximum a posteriori probability (MAP) forecasting is an efficient and robust method for the optimisation of drug therapy, but its use for anticancer drugs is not yet extensive. The aim of this paper is to review the application of population pharmacokinetics and MAP to anticancer drugs and to evaluate whether and when MAP Bayesian estimation improves the clinical benefit of anticancer chemotherapy. For each drug, the relationships between pharmacokinetic variables [e.g. plasma concentration or the area under the concentration-time curve] and pharmacodynamic effects are described. Secondly, the methodologies employed are considered and, finally, the results are analysed in terms of predictive performance as well as, where possible, the impact on clinical end-points. Some studies were retrospective and intended only to evaluate individual pharmacokinetic parameter values using very few blood samples. Among the prospective trials, a few studied the pharmacokinetic/pharmacodynamic relationships which provided the basis for routine pharmacokinetic monitoring. Others were performed in clinical context where MAP Bayesian estimation was used to determine maximum tolerated systemic exposure (e.g. for carboplatin, topotecan, teniposide) or for pharmacokinetic monitoring (e.g. for methotrexate or platinum compounds). Indeed, its flexibility in blood sampling times makes this technique much more applicable than other limited sampling strategies. These examples demonstrate that individual dose adjustment helps manage toxicity. The performance of pharmacokinetic monitoring is linked to the methodology used at each step of its design and application. Moreover, a limitation to the use of pharmacokinetic monitoring for certain anticancer drugs has been the difficulty in obtaining pharmacokinetic or pharmacodynamic data. Recent progress in analytical methods, as well as the development of noninvasive methods (such as positron emission tomography) for evaluating the effects of chemotherapy, will help to define pharmacokinetic-pharmacodynamic relationships. Bayesian estimation is the strategy of choice for performing pharmacokinetic studies, as well as ensuring that a given patient benefits from the desired systemic exposure. Together, these methods could contribute to improving cancer chemotherapy in terms of patient outcome and survival.

Antineoplastic chemotherapy of the older cancer patient

Cancer chemotherapy may be effective and safe in older patients if some proper provisions are made. Doses of chemotherapy should be adjusted to the patient's glomerular filtration rate, and his or her hemoglobin should be maintained for the duration of the therapy. For patients who are 70 years of age or older and who are receiving moderately toxic chemotherapy, growth factors should be used. The risk of mucositis increases with the age of the patient, so it is important to treat it aggressively at the first signs of the complication.

A study of the feasibility and accuracy of pharmacokinetically guided etoposide dosing in children

Pharmacokinetically guided dosing was performed in nine paediatric patients receiving etoposide. Doses on day 2 of a 2- or 3-day schedule were adapted on the basis of the day-1 area under the plasma etoposide concentration vs time curve (AUC). The day-1 AUC was estimated using a limited sampling model and the day-2 target AUC defined by the etoposide dose-AUC relationship observed in 33 children. Target AUC values (4.6-8.2 mg ml(-1) x min) were achieved with a high degree of precision and with little bias (mean error 11% and root mean squared error 15% respectively). Pharmacokinetic parameters were similar to those reported previously in children, although interpatient pharmacokinetic variability was less than that observed previously: plasma clearance, 23 (18-26) ml min(-1) m(-2); volume of distribution at steady state (Vdss), 6.0 (3.9-8.9) l m(-2); t(1/2) 254 (127-550) min (median and range). This study has demonstrated that pharmacokinetically guided dosing with etoposide is feasible. However, pharmacokinetically guided dosing is likely to be of most benefit in patients with abnormalities of renal or hepatic function, or in children with prior exposure to cisplatin.

Etoposide combined with interferon alfa-2b: novel exploitation of established etoposide pharmacokinetics and pharmacodynamics

PURPOSE

To construct an efficient pilot study design to determine whether interferon alfa-2b modifies the pharmacokinetics and pharmacodynamics of continuous-infusion etoposide.

PATIENTS AND METHODS

A two-stage randomized 2 X 2 factorial design was used to evaluate interferon alfa-2b at two doses (2 or 10 MU/m2/day SQ for 3 days) and two schedules (interferon alfa-2b administered before or concurrent with 72-hour continuous-infusion etoposide). Etoposide was administered at 75, 100, or 125 mg/m2/day. In lieu of comparing the experimental arms to an etoposide-alone control arm to determine effect of interferon alfa-2b dose and schedule, a novel analytic approach was used. The effect of interferon alfa-2b on etoposide-induced leukopenia was assessed indirectly by comparison of the observed white blood cell (WBC) nadir to the nadir predicted from an established pharmacodynamic model for single agent etoposide.

RESULTS

Based on 29 patients, dose-normalized 24-hour total and estimated free etoposide concentrations did not differ with interferon alfa-2b dose or schedule. Patients treated with interferon alfa-2b before etoposide had, on average a WBC nadir 545 +/- 225 cells microliter lower than that predicted by a pharmacodynamic model for etoposide alone. An optimal nonlinear model for leukopenia was defined by interferon alfa-2b schedule in addition to 24-hour etoposide concentration.

CONCLUSION

A novel study design and statistical analysis provided an efficient preliminary evaluation of the combination of interferon alfa-2b with etoposide in a modest number of patients. Exploitation of a previously validated pharmacodynamic model allowed evaluation of interferon alfa-2b effect and eliminated the need for an etoposide-alone control arm. The pharmacokinetics of continuous-infusion etoposide at doses from 75 to 125 mg/m2/day appear to be unchanged by interferon alfa-2b at the doses and schedules tested and the combination appears to be feasible. We hypothesize that leukopenia may be enhanced when interferon alfa-2b is administered before etoposide, especially at a higher dose of interferon alfa-2b.

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.

Etoposide: twenty years later

Since the beginning of its clinical development 20 years ago, etoposide has become an important and widely used agent in clinical oncology. Its integral role in the treatment of germ cell tumors and small-cell lung cancer seems unlikely to diminish in the future, and its use in non-Hodgkin's lymphoma and in various high dose regimens will probably continue to increase. Active investigation continues regarding the optimal dose and schedule of etoposide, and it is likely that these investigations will result in further improvement of its clinical activity in patients with sensitive tumor types. Continued clinical investigation may result in the identification of active etoposide containing combination regimens for ovarian cancer, breast cancer, and some of the childhood malignancies. Exciting possibilities for the future include exploration of etoposide in combination with the topoisomerase I inhibitors, as well as the development of drugs to reverse drug resistance. During the next 10 years, the applications and importance of this unique drug will continue to increase.

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.

Limited-sampling models for anticancer agents

Pharmacokinetic parameters of antineoplastic drugs are usually generated from concentration/time profiles obtained after multiple venipunctures. With limited-sampling models (LSM) this number can be reduced to between one and three timed plasma samples. LSMs may facilitate population pharmacokinetic/pharmacodynamic studies, which eventually may lead to a dosing strategy based on the characteristics of the individual patient. In this article, the development, validation and application of several LSMs reported in the literature are reviewed.

Limited sampling models for topotecan pharmacokinetics

BACKGROUND

Limited sampling models for the estimation of the topotecan Area Under the concentration versus time Curve (AUC) and its lactone ring opened form (AUC Tm), from one or more plasma concentration determinations, are desired for further population-kinetic studies.

PATIENTS AND METHODS

The models were developed and validated using 34 pharmacokinetic curves in 19 patients who participated in a phase I study.

RESULTS

A single point model was selected as optimal: AUC (mumol/L.min) = 499 (min).C2h (mumol/L) +0.85 (m2/mg.mumol/L.min).dose(mg/m2), and for topotecan-metabolite (Tm), AUC Tm (mumol/L.min) = 55.1 (min).CTm2h (mumol/L) -0.011 (m2/mg.mg.mumol/L.min).dose (mg/m2), where C2h is the plasma concentration (mumol/L) of topotecan at 2 h after the end of a 30-min infusion, and CTm2h the concentration of the opened form at the same time point. The models are valid for dosages ranging from 0.5 to 1.5 mg/m2/day and proved to be unbiased (MPE% = -1.8% and -9.3%, respectively) and precise (RMSE% = 17.9% and 22.7%, respectively). From the predicted AUCs, the clearance (Cl = dose (mumol)/AUC(mumol/L.min)) could also reliably be predicted, as well as the total AUC (AUC+AUC Tm) RMSE% = 17.1% and MPE% = -0.02%). Half-life values could not be predicted with acceptable precision and accuracy.

CONCLUSION

The limited sampling models presented may useful for future studies focused on pharmacokinetic/pharmacodynamic relationships of topotecan in large populations.

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.

Pharmacodynamics and long-term toxicity of etoposide

Etoposide has been used in the treatment of a wide variety of neoplasms, including small-cell lung cancer, Kaposi's sarcoma, testicular cancer, acute leukemia, and lymphoma. Its current therapeutic use is limited by myelosuppression, particularly neutropenia. Pharmacodynamic studies of etoposide show that this toxicity can be modeled using a modified Hill equation and that the dose intensity of etoposide can be successfully increased by adaptive control using this model. Significant influences on the degree of myelosuppression include the pretreatment leukocyte count, the performance status, the extent of prior erythrocyte transfusions, and the serum albumin level. In the past 7 years, interest has developed in a distinct subset of acute nonlymphocytic leukemia that is associated with prior exposure to etoposide. This syndrome has been described in several studies and is characterized by the lack of a preleukemic phase, M4 or M5 morphology, and distinct translocations involving the chromosome 11q23 region. In addition, secondary acute lymphocytic leukemias (involving 11q23) have also been associated with prior epipodophyllotoxin exposure.

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.

A limited sampling method for estimation of the etoposide area under the curve

A limited sampling method for estimation of the etoposide area under the curve (AUC) is presented. The method was developed and validated in 23 patients (42 pharmacokinetic studies) with small-cell lung cancer (SCLC), limited disease. The patients received 100 mg/m2 etoposide as a 90-min intravenous infusion in combination with carboplatin, allowing for etoposide dose modification at a following course (25% increase or decrease) due to high or low nadir values for leukocytes or thrombocytes. Of the 42 pharmacokinetic studies, 27 were used in the model development and 15 were used in the model validation. Single regression analyses of the AUC versus the fitted concentrations for the model data set were performed at several time points. The analyses demonstrated high and essentially identical correlation coefficients in the interval between 2 and 21 h, with a maximal value of 0.96 being recorded at 4 h. Multiple regression analysis was then performed using fitted concentrations corresponding to 0.08-21 h. The best model for one sample was AUC = 1.01 x (dose level divided by 100 mg/m2) + 799 x C4 h, that for two samples was AUC = 1.43 x (dose level divided by 100 mg/m2) + 544 x C4 h + 1756 x C21 h, and that for three samples was AUC = 0.07 x (dose level divided by 100 mg/m2) + 110 x C5 min + 474 x C4 h + 1759 x C21 h. Not unexpectedly, the model validation revealed that the one-sample model was less precise than the two- or three-sample model [percentage of root mean squared error (RMSE%) = 11.6%, 7.1%, and 5.4%, respectively]. All models proved to be unbiased in the validation [percentage of mean predictive error (MPE%) +/- SE = 4.2% +/- 11.0%, 7.9% +/- 6.1%, and 6.3% +/- 5.3%, respectively]. The models were subsequently validated in 14 pharmacokinetic studies of patients with metastatic germ-cell tumours who were receiving combination chemotherapy with cisplatin and bleomycin plus 100 mg/m2 etoposide as a 90-min infusion. The RMSE% was 13.4%, 10.8%, and 9.0% and the MPE% +/- SE was -1.0% +/- 11.9%, 1.7% +/- 10.5%, and 2.7% +/- 7.9% for the one-, two-, and three-sample models, respectively. The limited sampling methods presented herein may prove to be a most valuable tool for therapeutic drug monitoring in regimens in which etoposide is given in combination with carboplatin or with cisplatin and bleomycin.