A comparative pharmacokinetic study of doxorubicin and 4'-epi-doxorubicin in children with acute lymphocytic leukemia using a limited sampling procedure

Review of nutritional status, body composition, and effects of antineoplastic drug disposition

The overall survival for children with cancer in high income countries is excellent. However, there are many disparities that may negatively affect survival, which are particularly problematic in low income countries, such as nutritional status at diagnosis and throughout therapy. Nutritional status as well as concomitant foods, supplements, and medications may play a role in overall exposure and response to chemotherapy. Emerging science around the microbiome may also play a role and should be further explored as a contributor to disease progression and therapeutic response. This article highlights some of these issues and proposes additional areas of research relevant to nutritional status and pharmacology that are needed in pediatric oncology.

Clinical and preclinical evidence of sex-related differences in anthracycline-induced cardiotoxicity

Anthracyclines are very effective chemotherapeutic agents that are widely used to treat pediatric and adult cancer patients. Unfortunately, the clinical utility of anthracyclines is limited by cardiotoxicity. There are several established risk factors for anthracycline-induced cardiotoxicity (AIC), including total cumulative dose, very young and very old age, concomitant use of other cardiotoxic agents, and concurrent mediastinal radiation. However, the role of sex as a risk factor for AIC is not well defined. In pediatric cancer patients, most studies support the notion that female sex is a significant risk factor for AIC. Conversely, there is anecdotal evidence that female sex protects against AIC in adult cancer patients. The lack of consistency in study designs and the different definitions of cardiotoxicity preclude reaching consensus regarding the role of sex as a risk factor for AIC in both pediatric and adult cancer patients. Therefore, more clinical research using reliable techniques such as cardiac magnetic resonance imaging is needed to determine if there truly are sex differences in AIC. In adult preclinical rodent studies, however, there is unequivocal evidence that female sex confers significant protection against AIC, with a possible protective effect of female sex hormones and/or a detrimental role of the male sex hormones. Although findings of these rodent studies may not perfectly mirror the clinical scenario in adult anthracycline-treated cancer patients, understanding the mechanisms of this significant sexual dimorphism may reveal important cardioprotective mechanisms that can be therapeutically targeted.

Imaging of early modification in cardiomyopathy: the doxorubicin-induced model

Doxorubicin chemotherapy is effective and widely used to treat acute lymphoblastic leukemia. However, its effectiveness is hampered by a wide spectrum of dose-dependent cardiotoxicity including both morphological and functional changes, affecting primarily the myocardium. Non-invasive imaging techniques are used for the diagnosis and monitoring of these cardiotoxic effects. The purpose of this review is to summarize and compare the most common imaging techniques used in early detection and therapeutic monitoring of doxorubicin-induced cardiotoxicity and the suggested mechanisms of such side effects. Imaging techniques using echocardiography including conventional 2D and 3D echocardiography along with MRI sequences including Tagging, Cine, and quantitative MRI in detecting early myocardial damage are also reviewed. As there is a multitude of reported indices and imaging methods to assess particular functional alterations, we limit this review to the most relevant techniques based on their clinical application and their potential to early detection of doxorubicin-induced cardiotoxic effects.

Population pharmacokinetics of doxorubicin: establishment of a NONMEM model for adults and children older than 3 years

PURPOSE

The aim of the current investigation was to develop a population pharmacokinetic model for doxorubicin and doxorubicinol that could provide improved estimated values for the pharmacokinetic parameters clearance of doxorubicin, volume of distribution of the central compartment, clearance of doxorubicinol and volume of distribution of the metabolite compartment for adults and children older than 3 years. A further aim was to investigate the potential influence of the covariates body surface area, body weight, body height, age, body mass index, sex and lean body mass on the pharmacokinetic parameters.

METHODS

Three different datasets, two containing data from adults and one containing data from adults and children, were merged and the combined dataset was analysed retrospectively. In total, the combined dataset contained 934 doxorubicin and 935 doxorubicinol plasma concentrations from 82 patients [64 adults and 18 children (<18 years)]. With this combined dataset, a population pharmacokinetic model was developed, using NONMEM(®) 7.2 and a predefined model-building strategy. Different structural models, error models and estimation methods were tested, and the inter-individual and the inter-occasion variability (variability between separate (two or three) doxorubicin infusions) were tested. Using a subset of 52 patients, the influence of different covariates on the pharmacokinetic parameters was investigated. The pharmacokinetic parameter estimates obtained from doxorubicin concentrations with the best model were fixed, and an additional compartment for doxorubicinol was added to the model. With the final model for both substances, a potential age dependency and body mass index dependency of the clearance of doxorubicin and doxorubicinol as well as of the volumes of distribution of the central and the metabolite compartment were evaluated.

RESULTS

A four-compartment model best described the doxorubicin and doxorubicinol data of the combined dataset. This model included a proportional residual error model and an inter-individual variability on the clearance of doxorubicin, on the inter-compartmental clearances of the peripheral compartments, on the clearance of doxorubicinol and on the volumes of distribution of the central, one peripheral and the metabolite compartment. Furthermore, the body surface area as covariate on all pharmacokinetic parameters and an inter-occasion variability for the clearance of doxorubicin and the volume of distribution of the central compartment were incorporated in the model. For a patient with the body surface area of 1.8 m², the clearance of doxorubicin was 53.3 L/h (inter-individual variability 31%, inter-occasion variability 13%) and the volume of distribution of the central compartment was 17.7 L (inter-individual variability 19%, inter-occasion variability 21%), respectively. The residual variability of the model was 22% for doxorubicin and 26% for doxorubicinol. The clearance of doxorubicinol was estimated at 44 L/h (inter-individual variability 50%) and the volume of distribution of the metabolite compartment at 1,150 L (inter-individual variability 57%). The evaluation of a possible age dependency and body mass index dependency showed a trend to a smaller volume of distribution of the central compartment (normalised to the body surface area) and a higher volume of distribution of the metabolite compartment (normalised to the body weight) in younger patients.

CONCLUSIONS

A four-compartment NONMEM(®) model for doxorubicin and doxorubicinol adequately described the plasma concentrations in adults and children (>3 years). No pronounced effects of age on the clearance of doxorubicin or doxorubicinol were found, and the analysis did not support the modification of the dosing strategies presently used in children and adults.

Pharmacokinetics and Drug Dosing in Obese Children

OBJECTIVES

To review pharmacokinetics in obese children and to provide medication dosing recommendations.

METHODS

EMBASE, MEDLINE, and International Pharmaceutical Abstracts databases were searched using the following terms: obesity, morbid obesity, overweight, pharmacokinetics, drug, dose, kidney function test, creatinine, pediatric, and child.

RESULTS

We identified 10 studies in which the authors examined drug dosing or pharmacokinetics for obese children. No information was found for drug absorption or metabolism. Obese children have a higher percent fat mass and a lower percent lean mass compared with normal-weight children. Therefore, in obese children, the volume of distribution of lipophilic drugs is most likely higher, and that of hydrophilic drugs is most likely lower, than in normal-weight children. Serum creatinine concentrations are higher in obese than normal-weight children. Total body weight is an appropriate size descriptor for calculating doses of antineoplastics, cefazolin, and succinylcholine in obese children. Initial tobramycin doses may be determined using an adjusted body weight, although using total body weight in the context of monitoring serum tobramycin concentrations would also be an appropriate strategy. We found no information for any of the opioids; antibiotics such as penicillins, carbapenems, vancomycin, and linezolid; antifungals; cardiac drugs such as digoxin and amiodarone; corticosteroids; benzodiazepines; and anticonvulsants. In particular, we found no information about medications that are widely distributed to adipose tissue or that can accumulate there.

CONCLUSIONS

The available data are limited because of the small numbers of participating children, study design, or both. The number and type of drugs that have been studied limit our understanding of the pharmacokinetics in obese children. In the absence of dosing information for obese children, it is important to consider the nature and severity of a child's illness, comorbidities, organ function, and side effects and physiochemical properties of the drug. Extrapolating from available adult data is possible, as long as practitioners consider the effects of growth and development on the pharmacokinetics relevant to the child's age.

Effect of obesity on the pharmacokinetics of drugs in humans

The prevalence of obesity has dramatically increased in recent years and now includes a significant proportion of the world's children, adolescents and adults. Obesity is linked to a number of co-morbidities, the most prominent being type 2 diabetes mellitus. While many agents are available to treat these conditions, the current knowledge regarding their disposition in the obese remains limited. Over the years, both direct and indirect methodologies have been utilized to assess body composition. Commonly used direct measures include underwater weighing, skinfold measurement, bioelectrical impedance analysis and dual-energy x-ray absorptiometry. Unfortunately, these methods are not readily available to the majority of clinicians. As a result, a number of indirect measures to assess body composition have been developed. Indirect measures rely on patient attributes such as height, bodyweight and sex. These size metrics are often utilized clinically and include body mass index (BMI), body surface area (BSA), ideal bodyweight (IBW), percent IBW, adjusted bodyweight, lean bodyweight (LBW) and predicted normal weight (PNWT). An understanding of how the volume of distribution (V(d)) of a drug changes in the obese is critical, as this parameter determines loading-dose selection. The V(d) of a drug is dependent upon its physiochemical properties, the degree of plasma protein binding and tissue blood flow. Obesity does not appear to have an impact on drug binding to albumin; however, data regarding alpha(1)-acid glycoprotein binding have been contradictory. A reduction in tissue blood flow and alterations in cardiac structure and function have been noted in obese individuals. At the present time, a universal size descriptor to describe the V(d) of all drugs in obese and lean individuals does not exist. Drug clearance (CL) is the primary determinant to consider when designing a maintenance dose regimen. CL is largely controlled by hepatic and renal physiology. In the obese, increases in cytochrome P450 2E1 activity and phase II conjugation activity have been observed. The effects of obesity on renal tubular secretion, tubular reabsorption, and glomerular filtration have not been fully elucidated. As with the V(d), a single, well validated size metric to characterize drug CL in the obese does not currently exist. Therefore, clinicians should apply a weight-normalized maintenance dose, using a size descriptor that corrects for differences in absolute CL between obese and non-obese individuals. The elimination half-life (t((1/2))) of a drug depends on both the V(d) and CL. Since the V(d) and CL are biologically independent entities, changes in the t((1/2)) of a drug in obese individuals can reflect changes in the V(d), the CL, or both. This review also examines recent publications that investigated the disposition of several classes of drugs in the obese--antibacterials, anticoagulants, antidiabetics, anticancer agents and neuromuscular blockers. In conclusion, pharmacokinetic data in obese patients do not exist for the majority of drugs. In situations where such information is available, clinicians should design treatment regimens that account for any significant differences in the CL and V(d) in the obese.

Long-Term Health Status Among Survivors of Childhood Cancer: Does Sex Matter?

Increasing numbers of children diagnosed with cancer will survive their primary malignancy. Within this growing population of long-term survivors, considerable effort has been put forth to identify treatment-related risks for adverse health-related outcomes, such as exposure to alkylating agents, anthracyclines, radiotherapy, and surgery. Patient sex has been identified as a risk factor for numerous long-term adverse outcomes, with female sex more commonly associated with higher risks. In this article, we review the literature, which generally supports associations between female sex and cognitive dysfunction after cranial irradiation, cardiovascular outcomes, obesity, radiation-associated differences in pubertal timing, development of primary hypothyroidism, breast cancer as a second malignant neoplasm and suggests an increased prevalence for the development of osteonecrosis among females. Results of this review support future investigations to further define sex as a risk factor for other common treatment-specific exposures and outcomes. Additionally, research should focus on understanding the underlying biologic and physiological basis of these sex-specific risks. Historically, evidence from both basic science and clinical research has been used to develop risk-stratified therapy, allowing reduction of toxic therapies to low-risk patients without compromising overall survival. With greater knowledge of sex-specific risks, the potential application of sex-specific therapy designed to avoid poor long-term adverse outcomes may become a viable strategy.

Pharmacokinetics of doxorubicin and etoposide in a morbidly obese pediatric patient

This case report presents the pharmacokinetics of doxorubicin and etoposide in a 14-year-old morbidly obese (body mass index: 46.3 kg/m2) male patient with Hodgkin disease. Dosing based on an adjusted body surface area resulted in a dose reduction by approximately 25% as compared to dosing based on actual body surface area. Plasma clearance of doxorubicin as well as plasma clearance and elimination rate of etoposide for this patient was comparable to pharmacokinetic data from nonobese pediatric patients. The therapy was well tolerated without any specific toxicity and a complete response was obtained after 2 scheduled courses, with the patient in complete remission 25 months after end of treatment.

Predictive factors of histologic response to primary chemotherapy in patients with Ewing sarcoma

A correlation between chemotherapy-induced necrosis and prognosis has been reported in Ewing sarcoma. To identify factors influencing histologic response data from 122 patients with Ewing sarcoma surgically treated were reviewed. Primary chemotherapy was based on vincristine, doxorubicin, cyclophosphamide, ifosfamide, actinomycin-D, and etoposide. Patients with complete necrosis or only scattered foci of viable tumor cells were good responders (GRs), the remaining patients poor responders (PRs). Age, sex, site and size of the tumor, fever at diagnosis, and lactate dehydrogenase level were clinical variables investigated. Mean age was 13.3+/-6 in GR and 18.1+/-9 in PR (P<0.0005); GR rate was 71% in patients<or=14 years, 39% in patients aged 15 to 18 years, and 26% in patient>18 years (P=0.003). Female were more likely to achieve a GR (F 64% vs. M 42%, P<0.02). After multivariate analysis sex and age retained statistical significance. Age and sex influence the histologic response in patients with Ewing sarcoma.

Doxorubicin pharmacokinetics is correlated to the effect of induction therapy in children with acute myeloid leukemia

We studied the pharmacokinetics of doxorubicin in 41 children treated for newly diagnosed acute myeloid leukemia. Doxorubicin, 75 mg/m2 body surface area, was administered by constant i.v. infusion over 8 h. Four children with Down's syndrome (DS), 1.2-2.3 years old, had a median total body clearance of 523 ml/min/m2. The median clearance in non-DS children, 0.6-1.8 years old (n = 4) and 2.5-17.7 years old (n = 33), was 446 and 538 ml/min/m2, respectively. Patients who went into complete remission (CR) after induction therapy had a significantly higher median plasma concentration of doxorubicin than those who did not, 249 compared with 180 ng/ml, respectively (P = 0.036; analysis restricted to non-DS patients). Doxorubicin plasma concentration was an independent factor for CR, both in univariate (P = 0.031) and multivariate analysis including sex, age and white blood cell count at diagnosis (P = 0.021). Patients who reached CR had a significantly lower doxorubicin clearance than those who did not, 513 and 657 ml/min/m2, respectively (P = 0.017). In conclusion, doxorubicin plasma concentration and total body clearance during up-front treatment were correlated to the effect of induction therapy. Prospective studies should be performed to confirm the concentration-effect relationship and explore the possibility of therapeutic monitoring.

Pharmacokinetics of doxorubicin in children with acute lymphoblastic leukemia: multi-institutional collaborative study

BACKGROUND

In adults, it has been shown that the pharmacokinetics of doxorubicin are highly variable, despite standardization of the dose based on body surface area (BSA). The purpose of this study was to determine the plasma concentrations of doxorubicin and its active metabolite doxorubicinol in children treated for acute lymphoblastic leukemia (ALL).

PROCEDURE

Children, 107 in number, aged 1.3-17.3 years, were studied at Day 1 of induction therapy according to the current Nordic protocol. Five infants, 3-9 months old, were also included. Plasma samples were drawn 23 hr after the start of a 24-hr infusion of doxorubicin 40 mg/m(2), and analyzed by reversed-phase liquid chromatography.

RESULTS

There was a more than 10-fold difference between patients in dose normalized plasma concentration of doxorubicin, median 62.8 ng/ml, range 22.6-334 ng/ml. The doxorubicin concentrations differed significantly between age groups (P = 0.003). Children aged 4-6 years had the highest doxorubicin concentrations, median 77.9 ng/ml, followed by 2-4-year-old children, median 64.3 ng/ml. Both younger and older children had median values of about 50 ng/ml. Patients with white blood cell (WBC) count > 50 x 10(9)/L at diagnosis had significantly lower doxorubicin concentrations, median 55.3 ng/ml, than those with WBC count < 10 x 10(9)/L, median 64.4 ng/ml (P = 0.015). There was no difference in doxorubicin concentration between boys and girls. No correlation was found between doxorubicin levels and serum aminotransferases or serum creatinine. The concentration of doxorubicinol was 13% (median value) of that of doxorubicin. Four infants, 7-9 months old, had plasma clearance between 350-431 ml/min/m(2), which is in the same range as in older children. A 3-month-old infant had a clearance of 181 ml/min/m(2).

CONCLUSIONS

The age groups who had the highest doxorubicin concentrations, (2-) 4-6-year-old children, are known to make up a large proportion of standard risk ALL cases with good prognosis. The correlation between doxorubicin plasma levels and clinical effect needs further study. The influence of age, body composition, and tumor burden on the pharmacokinetics of antineoplastic drugs should also be further explored, aiming at improvements in the current dosing regimen based on BSA.

Pharmacokinetics of acyclovir in immunocompromized children with leukopenia and mucositis after chemotherapy: can intravenous acyclovir be substituted by oral valacyclovir?

BACKGROUND

The efficacy of oral acyclovir, a purine nucleoside analogue with activity against human herpes viruses, is limited as a result of its low bioavailability. Valacyclovir, the L-valyl ester of acyclovir, has been developed as a pro-drug to improve the bioavailability. The aim of the present study was to compare the pharmacokinetics of acyclovir after intravenous administration and after oral administration of valacyclovir.

PROCEDURE

The pharmacokinetics of acyclovir were studied in 18 children aged 1.4-18.1 years (median: 6.9 years; 9 females) after intravenous infusion (1 hr; median dose: 10.5 mg/kg). In 10 of the children the pharmacokinetics of acyclovir were also studied after oral administration of valacyclovir (median dose: 34.1 mg/kg). Quantification of acyclovir in serum was performed by reversed-phase liquid chromatography with fluorometric detection. The pharmacokinetic analysis was performed by pharmacokinetic modelling.

RESULTS

The serum concentration versus time curves of acyclovir were described by the two compartment model after intravenous administration and by the one compartment model with a zero- or first-order absorption phase after oral administration of valacyclovir. The bioavailability of acyclovir after oral administration of valacyclovir was 45% (median value; 95% CI: 37-55%).

CONCLUSION

It is possible to substitute intravenous acyclovir therapy by oral valacyclovir therapy in children with leukopenia and mucositis after chemotherapy. This finding can at present not be fully implemented in clinical practice, since a commercial pharmaceutical formulation of valacyclovir aimed for children not able to swallow intact tablets is lacking. Crushed valacyclovir tablets have a very unpleasant taste, but can be administered to children through nasogastric tubes.

Quantification of doxorubicin in plasma--a comparative study of capillary and venous blood sampling

Doxorubicin, an anthraquinone glycoside, is currently one of the clinically most important antineoplastic drugs. The aim of the present study was to identify potential concentration differences of doxorubicin in plasma from capillary and venous blood samples. Sixteen patients (seven females and nine males; median age: 37 years, range: 1-77 years) were included. The quantitative analysis of doxorubicin was carried out by reversed-phase liquid chromatography with fluorometric detection. The concentration of doxorubicin in capillary and venous samples were closely correlated (r=0.98; p<0.0001). The median plasma concentration ratio capillary/venous was 1.13 (95% confidence interval: 1.06-1.20) and not affected either by plasma drug concentration, age or the body mass index of the patient. The concentration ratio was significantly higher in males (median: 1.18) than in females (median: 1.01). The observed concentration differences of doxorubicin in plasma from capillary and venous samples are of minor importance only. Capillary blood sampling is recommended for use in pharmacokinetic studies of doxorubicin, especially in pediatric patients, in order to avoid sometimes traumatic venous blood sampling.