Phase I trial and pharmacokinetic study of ixabepilone administered daily for 5 days in children and adolescents with refractory solid tumors

Purpose: The objectives of this phase I trial were to determine the maximum-tolerated dose (MTD), toxicity profile, dose-limiting toxicities (DLTs), pharmacokinetics, and preliminary response rate for ixabepilone, a microtubule-stabilizing agent, administered intravenously daily for 5 days in children and adolescents. Patients and Methods: Patients ≥ 2 and ≤ 18 years with relapsed or refractory solid tumors were enrolled onto sequential cohorts to the following five dose levels: 3.0 (n = 3), 4.5 (n = 4), 6.0 (n = 3), 8.0 (n = 6), and 10 (n = 3) mg/m²/d. Eligibility criteria, dose levels, definitions of DLT and MTD, and pharmacokinetic sampling times were designed to be as similar as possible to the adult phase I trial of ixabepilone on the same schedule. Results: Nineteen children (median age, 10 years; range, 2 to 18 years) were enrolled, and 18 (12 with sarcomas) were assessable for toxicity. DLTs (grade 4 neutropenia for > 5 days and grade 3 fatigue) were observed in two of three patients receiving 10 mg/m2/d. The MTD of ixabepilone administered daily for 5 days every 21 days was 8 mg/m²/d. Myelosuppression, GI, and hepatic toxicities were common non-DLTs. Peripheral neuropathy was uncommon. Ixabepilone clearance was 475 ± 247 mL/min/m², volume of distribution at steady-state was 12.2 ± 5.4 L/kg, and half-life was 14 hours. Conclusion The recommended dose of ixabepilone for phase II trials in solid tumors is 8 mg/m²/d daily for 5 days every 21 days. This dose is 33% higher than the MTD in adults receiving the same dosing schedule. Pharmacokinetic parameters in children and adolescents were highly variable but similar to adults.