Low dose--high dose: what is the right dose? Pharmacokinetic modeling of etoposide

Utility of a next-generation framework for assessment of genomic damage: A case study using the pharmaceutical drug candidate etoposide

We present a hypothetical case study to examine the use of a next-generation framework developed by the Genetic Toxicology Technical Committee of the Health and Environmental Sciences Institute for assessing the potential risk of genetic damage from a pharmaceutical perspective. We used etoposide, a genotoxic carcinogen, as a representative pharmaceutical for the purposes of this case study. Using the framework as guidance, we formulated a hypothetical scenario for the use of etoposide to illustrate the application of the framework to pharmaceuticals. We collected available data on etoposide considered relevant for assessment of genetic toxicity risk. From the data collected, we conducted a quantitative analysis to estimate margins of exposure (MOEs) to characterize the risk of genetic damage that could be used for decision-making regarding the predefined hypothetical use. We found the framework useful for guiding the selection of appropriate tests and selecting relevant endpoints that reflected the potential for genetic damage in patients. The risk characterization, presented as MOEs, allows decision makers to discern how much benefit is critical to balance any adverse effect(s) that may be induced by the pharmaceutical. Interestingly, pharmaceutical development already incorporates several aspects of the framework per regulations and health authority expectations. Moreover, we observed that quality dose response data can be obtained with carefully planned but routinely conducted genetic toxicity testing. This case study demonstrates the utility of the next-generation framework to quantitatively model human risk based on genetic damage, as applicable to pharmaceuticals.

Towards a Model-Based Dose Recommendation for Doxorubicin in Children

Following the publication of our paper regarding a population-based model of doxorubicin pharmacokinetics in children in Clinical Pharmacokinetics last year (Voller et al. 54:1139-1149, 2015), we have received many inquiries on the practical clinical consequences of this model; however, a population-based model is only one of the aspects to be taken into account when developing dosing algorithms. In addition, any new method of dose calculation would need clinical validation and, subsequently, a new clinical trial. However, such a trial, especially with regard to burden to the children involved, requires optimal preparation and the selection of the best hypotheses. The European Paediatric Oncology Off-Patent Medicines Consortium (EPOC), represented by the authors, would therefore like to initiate an interdisciplinary discussion on the clinical and pharmacological goals for dose calculation. This current opinion summarizes the existing knowledge on the pharmacokinetics and pharmacodynamics of doxorubicin. Our aim was to define the clinical needs as precisely as possible, with the intention of stimulating discussion between the clinical pediatric oncologist and the pediatric pharmacologist. By doing so, we hope to define surrogates for best practice of a common doxorubicin dose in children. The intent is for a trial to validate a rational dose calculation rule, leading to a regulatory process and subsequent labeling.

Treatment of children with poor risk solid tumors by further escalation of the VETOPEC regimen including very high-dose cyclophosphamide and peripheral stem cell support: an Australian and New Zealand Children's Hematology and Oncology Group study

BACKGROUND

Children with solid tumors deemed to be poor risk at diagnosis and those who fail to respond or recur after chemotherapy have adverse outcomes. We sought to increase the dosage of cyclophosphamide (CPA) in the VETOPEC regimen (vincristine, etoposide, and CPA) with a view to improving the response rate and survival.

PROCEDURE

Patients underwent peripheral blood stem cell (PBSC) harvest after standard dose VETOPEC (CPA 40 mg/kg/day for 3 days) followed by filgrastim. Those with sufficient PBSC received up to four intensive cycles (ICs) of VETOPEC with CPA dosages of 60-90 mg/kg/day for 3 days (escalated by 5 mg/kg/day in cohorts of at least five patients) followed by PBSC and filgrastim.

RESULTS

Of the 59 enrolled patients, 58 were treated with mobilization chemotherapy and 57 proceeded to PBSC harvest. From 1 to 4 VETOPEC ICs were administered to 51 patients. The maximum tolerated dosage of CPA was not reached. The best response rate during the ICs for patients with recurrent or refractory/progressive disease was 67%; overall survival was 28% at 5 years and 25% at 10 years. The response rate for patients with newly diagnosed high-risk tumors was 89%.

CONCLUSIONS

The VETOPEC regimen with CPA dosages up to 90 mg/kg/day for 3 days followed by PBSC and filgrastim can be given in a timely manner with manageable toxicity. Outcomes were not improved when compared to prior VETOPEC studies. VETOPEC produces high response rates and warrants further evaluation in appropriate patients with newly diagnosed high-risk solid tumors.

Modeling the Pharmacodynamics of Highly Schedule-Dependent Agents: Exemplified by Cytarabine-Based Regimens in Acute Myeloid Leukemia

BACKGROUND

Many agents in antineoplastic chemotherapy are highly schedule dependent. Therefore, variables such as total dose and also the area under the curve (AUC) that are schedule insensitive are generally insufficient to adequately represent treatment strength.

PURPOSE

To establish a descriptor of treatment strength that takes into account the differential contribution of plasma concentrations (C) and exposure times (T) towards the cytotoxic effect and to investigate whether such a pharmacodynamically weighed descriptor is better correlated to the clinical effect than conventional variables.

PATIENTS AND METHODS

The paradigm "C(N) x T = constant" (for an isoeffect) incorporates a weighing factor N (concentration coefficient) into the conventional description of the AUC that quantitates the differential contribution of C and T towards the cytotoxic effect. N was to be numerically derived from a multitude of in vitro isoeffect analyses of the major agents in acute myeloid leukemia (AML) therapy from patient samples (n = 57).

RESULTS

For cytarabine, N was 0.45, numerically expressing the substantially higher relevance of T versus C for its cytotoxic effect. In a meta-analysis of 49 study arms involving >10,000 patients, neither total dose, dose intensity, nor AUC was correlated to the clinical effect. However, when AUC was pharmacodynamically weighed (N-weighed AUC, N-AUC = C(0.45) x T), this new descriptor was highly significantly correlated to the clinical effect (P < 0.001).

CONCLUSION

The N-AUC concept is able to characterize schedule-dependent agents and is the only descriptor of cytarabine treatment strength actually correlated to the clinical effect in AML.