Purpose: To determine the maximum-tolerable dose (MTD) and to investigate the pharmacokinetics and pharmacodynamics of topotecan in a phase I study. Topotecan is a novel semisynthetic derivative of the anticancer agent camptothecin and inhibits the intranuclear enzyme topoisomerase I. Broad preclinical activity rationalized further clinical evaluation.
Patients and methods: In this phase I trial, topotecan was administered by 24-hour continuous infusion every 21 days to patients with solid malignant tumors.
Results: A total of 25 eligible patients, of whom 22 were pretreated, entered the study. They received the following dosages of topotecan: 2.5, 3.75, 5.60, 8.4, and 10.5 mg/m2 by 24-hour infusion. Reversible leukopenia and thrombocytopenia were dose-limiting, with mild anemia occurring regularly. Other toxicities, such as alopecia, mucositis, nausea, and vomiting were sporadic and mild. Responses were not observed. However, eight patients had stable disease. The plasma concentration-time curves were not compatible with standard linear pharmacokinetic models, and indications were found for the occurrence of nonlinear (saturation) kinetics at the dosages studied.
Conclusion: The recommended dose for phase II studies is 8.4 mg/m2 when administered as a 24-hour infusion, which is well tolerated. Further studies will be necessary to account for the putative nonlinear behavior of the drug.