Purpose: To assess the safety and toxicity profile of escalating doses of intravenous irinotecan, in combination with a fixed dose of oral ciclosporin (Cs) and to determine the pharmacokinetic profile of irinotecan and its metabolites.
Patients and methods: Patients with fluorouracil-refractory metastatic colorectal cancer received escalating doses of intravenous irinotecan from 40 to 125 mg/m(2) every 2 weeks in combination with a fixed dose of oral Cs (5 mg/kg bid for 3 days). Pharmacokinetic analysis of plasma irinotecan and its metabolites SN38 and SN38G was performed during paired cycles with and without Cs.
Results: Thirty-seven patients were treated. Dose-limiting toxicity of grade 4 neutropenia was seen at an irinotecan dose of 125 mg/m(2). There was no grade 4 diarrhea, and only one patient experienced grade 3 diarrhea. Toxicities caused by Cs were generally mild. Pharmacokinetic studies demonstrated that irinotecan clearance was reduced from 13.4 to 5.8 L/h/m(2) and area under the curve (AUC)(0-tn) was increased 2.2-fold by the coadministration of Cs. Similar significant increases in AUC(0-24h) were seen for both SN38 and SN38G (2.2-fold and 2.3-fold, respectively) in the presence of Cs. Antitumor activity was seen at every irinotecan dose level.
Conclusion: The maximum tolerated irinotecan dose and recommended dose for phase II studies is 100 mg/m(2) every 2 weeks. Dose-limiting diarrhea was not seen during this study, supporting the hypothesis that pharmacokinetic modulation of irinotecan by Cs may improve its therapeutic index. Further studies using this combination are warranted.