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Using Pharmacokinetic and Pharmacodynamic Modeling and Simulation to Evaluate Importance of Schedule in Topotecan Therapy for Pediatric Neuroblastoma

Authors' Affiliations: Departments of ¹ Pharmaceutical Sciences and ² Oncology, St. Jude Children's Research Hospital; and Departments of ³ Pharmaceutical Sciences and ⁴ Pediatrics, University of Tennessee Health Sciences Center, Memphis, Tennessee

Requests for reprints: Clinton F. Stewart, Department of Pharmaceutical Sciences, St. Jude Children's Research Hospital, 332 North Lauderdale, Memphis, TN 38105-2794. Phone: 901-495-3665; Fax: 901-525-6869; E-mail: Clinton.stewart{at}stjude.org.

Purpose: The study aims to use mathematical modeling and simulation to assess the relative contribution of topotecan systemic exposure and scheduling in the activity and myelosuppression of topotecan in pediatric patients with neuroblastoma.

Experimental Design: Pharmacokinetic and pharmacodynamic data were obtained from a phase II study for pediatric patients with high-risk neuroblastoma. The topotecan dosage was individualized to attain a topotecan lactone area under the plasma concentration-time curve between 80 and 120 ng/mL h and given over a protracted schedule (i.e., 10 days). Four mathematical models describing topotecan pharmacokinetics, tumor growth, and neutrophil and platelet dynamics were developed. The models were combined to simulate and compare different topotecan treatment strategies with respect to systemic exposure and schedule.

Results: The median change in tumor volume was significantly different between schedules (5% increase for D x 5 versus 60% decrease for D x 5 x 2; P < 0.0001) when administering the same total systemic exposure. Whereas protracted schedules showed increased neutropenia (median of 7 versus 12 days below an absolute neutrophil count of 500/µL; P < 0.0001) and thrombocytopenia (median of 3 versus 10 days below a platelet count of 20,000/µL; P < 0.00001), simulations showed that delays in topotecan therapy would not be required. Simulations showed that an increase in topotecan exposure on the D x 5 schedule by 2.4-fold resulted in a modest decrease in tumor volume (i.e., median percentage change tumor volume of 24% versus 3%).

Conclusions: The present mathematical model gave an innovative approach to determining relevant topotecan schedules for possible evaluation in the clinic, which could lead to improved tumor response with minimized toxicities.