ABSTRACT
Pharmacodynamic measures of neutropenia, such as absolute neutrophil count at nadir and neutrophil survival fraction, may not reflect the overall time course of neutropenia. We developed a pharmacokinetic-pharmacodynamic model to describe and quantify the time course of neutropenia after administration of topotecan to children and to compare this with nonhuman primates (NHPs) as a potential preclinical model of neutropenia. Topotecan was administered as a 30-min infusion daily for 5 days, repeated every 21 days. As part of a Phase I Pediatric Oncology Group study, topotecan was administered at 1.4 and 1.7 mg/m(2)/day without filgrastim (POG), and at 1.7, 2, and 2.4 mg/m(2)/day with filgrastim (POG+G). In NHPs, topotecan was administered at 5, 10, and 20 mg/m(2)/day without filgrastim. A pharmacokinetic-pharmacodynamic model was fit to profiles of topotecan lactone plasma concentrations and neutrophil survival fraction from cycle 1 and used to calculate topotecan lactone area under the plasma concentration-versus-time curve from 0 to 120 h (AUC(LAC)) and the area between the baseline and treatment-related neutrophil survival fraction (ABC) from 0 to 700 h. The mean +/- SD neutrophil survival fraction at nadir for the POG, POG+G, and NHP groups was 0.12 +/- 0.09, 0.11 +/- 0.17, and 0.09 +/- 0.08, respectively (P > 0.05). The mean +/- SD for the ratio of ABC to AUC(LAC) for the POG and NHP groups was 1.02 +/- 0.38 and 0.16 +/- 0.09, respectively (P < 0.05). The model estimate of ABC and the ratio of ABC to AUC(LAC) in children and NHPs may better reflect sensitivity to chemotherapy-induced neutropenia.
Subject(s)
Neutropenia/pathology , Topotecan/pharmacokinetics , Animals , Antineoplastic Combined Chemotherapy Protocols/therapeutic use , Area Under Curve , Child , Child, Preschool , Clinical Trials, Phase I as Topic , Disease Models, Animal , Female , Filgrastim , Granulocyte Colony-Stimulating Factor/administration & dosage , Humans , Male , Metabolic Clearance Rate , Neoplasms/drug therapy , Neoplasms/metabolism , Neutropenia/chemically induced , Neutropenia/metabolism , Neutrophils/drug effects , Recombinant Proteins , Time Factors , Topoisomerase I Inhibitors , Topotecan/administration & dosage , Topotecan/adverse effectsABSTRACT
Gemcitabine (dFdC) is a prodrug that undergoes metabolism by cytidine deaminase to form an inactive metabolite, 2',2'-difluorodeoxyuridine (dFdU). The pharmacokinetics of dFdC and dFdU have been studied; however, their disposition has never been evaluated in a patient with ascites. A patient with pancreatic cancer and malignant ascites was treated with dFdC 1,500 mg/m2 over 150 minutes weekly for 3 weeks, repeated every 4 weeks. Serial plasma and ascites samples were obtained on weeks 1 and 2 of cycle 2. High-pressure liquid chromatography was used to quantify dFdC and dFdU in plasma and ascites. The systemic dispositions of dFdC and dFdU were similar to those reported in patients without ascites. The concentration of dFdC in ascites approached 1 mg/ml. Ascitic fluid did not serve as a depot for dFdC, and the agent's concentration in ascites approached that at which its phosphorylation is saturated.
