Phase I and pharmacologic study of irinotecan administered as a 96-hour infusion weekly to adult cancer patients

Purpose: We conducted a phase I and pharmacologic study of a weekly 96-hour infusion of irinotecan ta determine the maximum-tolerated dose, define the toxicity profile, and characterize the clinical pharmacology of irinotecan and its metabolites. Patients and Methods: In 26 adult patients with solid tumors, the duration and dose rate of infusion were escalated in new patients until toxicity was observed. Results: In 11 patients who were treated with irinotecan at 12.5 mg/m(2)/d for 4 days weekly for 2 of 3 weeks, dose-limiting grade 3 diarrhea occurred in three patients and grade 3 thrombocytopenia occurred in two patients. T he recommended phase II dose is 10 mg/m2/d for 4 days given weekly for 2 of 3 weeks. At this dose, the steady-state plasma concentration (Css) of tota l SN-38 (the active metabolite of irinotecan) was 6.42 +/- 1.10 nmol/L, and the Css of total irinotecan was 28.60 +/- 17.78 nmol/L. No patient experie nced grade 3 or 4 neutropenia during any cycle. All other toxicities were m ild to moderate. The systemic exposure to SN-38 relative to irinotecan was greater than anticipated, with a molar ratio of the area under the concentr ation curve (AUC) of SN-38 to irinotecan of 0.24 +/- 0.08. One objective re sponse lasting 12 months in duration was observed in a patient with metasta tic colon cancer. Conclusion: The recommended phase II dose of irinotecan of 10 mg/m(2)/d for 4 days weekly for 2 of 3 weeks was extremely well tolerated. Further effic acy testing of this pharmacologic strategy of administering intermittent lo w doses of irinotecan is warranted. J Clin Oncol 18:659-667. (C) 2000 by Am erican Society of Clinical Oncology.