Phase I clinical and pharmacological study of 72-hour continuous infusion of etoposide in patients with advanced cancer.

Etoposide (VP-16) is a semisynthetic epipodophyllotoxin that exhibits cell cycle phase specific cytotoxicity and enhanced effectiveness with increasing duration of drug exposure. We have therefore conducted a Phase I trial to determine the side effects, tolerable doses, and pharmacokinetic parameters of VP-16 given by continuous i.v. infusion to patients with advanced cancer. Eighteen patients were treated with varying dosages of VP-16 infused continuously for 72 consecutive hours every 28 days. Using this schedule, the maximally tolerated dosage of VP-16 was 150 mg/m2/day for patients with good performance status and 125 mg/m2/day for more debilitated cancer patients. Hematological toxicity was dose limiting with median granulocyte and platelet nadirs of 700/mm3 and 116,000/mm3, respectively, at a dose of 150 mg/m2/day. Other toxicities included only mild nausea, vomiting, and alopecia. Plasma and urine VP-16 concentrations were determined using a high-performance liquid chromatography assay. At a VP-16 dosage of 150 mg/m2/day, steady-state VP-16 concentrations were in the range of 2.1 to 7.0 micrograms/ml in all patients. Further pharmacokinetic analysis revealed that the plasma clearance of VP-16 was consistently near 25 ml/min/m2 (independent of dosage) and that renal clearance accounted for only 15% of VP-16 total plasma clearance. Patient age was found to be the most important factor correlating with plasma clearance of VP-16. Linear regression analysis also revealed that both the plasma VP-16 concentration at steady state and the concentration of VP-16 in plasma at 24 h from the start of the infusion correlated with hematological toxicity; no other patient characteristics correlated with hematological toxicity. The recommended VP-16 dose for Phase II trials of 72-h continuous infusion VP-16 is 150 mg/m2/day in patients with good performance status.