A phase I/II trial and pharmacokinetic study of ixabepilone in adult patients with recurrent high-grade gliomas

Ixabepilone is an epothilone, a novel class of non-taxane microtubule stabilizing agents. A phase I/II and pharmacokinetic trial of ixabepilone was conducted in patients with recurrent high-grade gliomas. Adult patients received ixabepilone as a 1-h infusion daily for 5 days every 3 weeks. A modified continual reassessment method was used to escalate doses, beginning at 5.0 mg/m², in patients stratified by use or non-use of enzyme inducing antiepileptic drugs (EIAED). In the phase I study, the maximum tolerated dose (MTD) and pharmacokinetics of ixabepilone were determined for each group. The phase II study used a two-stage design to evaluate response rate. Secondary endpoints were survival and 6-month progression free survival. In the phase I trial, 38 patients (median age 54 years) were enrolled. The MTD was 6.8 mg/m² for patients not taking EIAEDs and 9.6 mg/m² for those taking EIAEDs. The dose limiting toxicities in both groups were hematologic. Twenty-three patients (median age 54 years) were enrolled in the first stage of the phase II trial. No objective responses were observed. Median overall survival was 5.8 (95% CI, 5.0–8.6) months and 6-month PFS rate was 4% (95% CI, 0–22%). The overall mean total body clearance for ixabepilone was significantly higher (P = 0.003) in patients receiving EIAEDs (36 ± 11 l/h/m²) than those not (24 ± 9.2 l/h/m²). Patients on EIAEDs had a substantially higher MTD likely due to induction of cytochrome P450. Ixabepilone had no activity in patients with recurrent high-grade gliomas.