Purpose: Etoposide has schedule-dependent cytotoxic activity, and clinical resistance may be overcome with prolonged low-dose therapy. Oral bioavailability is variable, and protracted intravenous administration is limited by water insolubility, which requires large infusion volumes. Etoposide phosphate (EP) is a water-soluble prodrug that is rapidly converted in vivo to etoposide, and may be administered in concentrated solution. A phase I study was conducted to determine the toxicity, pharmacokinetics, and pharmacodynamics of EP administered as a protracted venous infusion in the ambulatory setting.
Methods: Twenty-three patients with advanced cancer were treated with a continuous infusion of EP using ambulatory pumps for 6 weeks followed by a 2-week rest. Cohorts were treated with EP at 10, 20, 25, and 30 mg/m2/d. Steady-state plasma etoposide levels (Css) and stability of EP in infusion pumps were measured using high performance liquid chromatography (HPLC).
Results: Myelosuppression, mucositis, and fatigue were dose-limiting. The maximum-tolerated dose (MTD) of EP was 20 mg/m2/d. The mean Css (+/- SD) of etoposide were 0.67 +/- 0.25, 1.14 +/- 0.24, 1.38 +/- 0.64, and 2.19 +/- 0.52 microg/mL at daily EP doses of 10, 20, 25, and 30 mg/m2, respectively. Neutropenia correlated with Css (r = 0.65, P = .008). EP was stable in infusion pumps for at least 7 days. Partial responses were observed in patients with hepatoma and non-small-cell lung cancer (one each).
Conclusion: EP may be conveniently and safely administered as a low-volume protracted venous infusion in the ambulatory setting. Cytotoxic plasma concentrations of etoposide are obtained at the MTD. The pharmacodynamic relationships observed suggest the possibility of pharmacologically based dosing of EP.