Phase I study of oral etoposide in children with refractory solid tumors

To determine the maximum-tolerated dose (MTD), dose-limiting toxicity, and plasma concentrations of orally administered etoposide (VP-16) in pediatric oncology patients.

In a phase I study, 20 children with refractory solid tumors received oral VP-16 (the intravenous preparation diluted with sodium chloride) three times daily for 21 days. Daily dose levels studied were 50 mg/m2 (n = 5), 60 mg/m2 (n = 7), and 75 mg/m2 (n = 8). VP-16 concentrations were measured in blood samples collected on days 1, 7, 14, and 21.

Grade 3 to 4 thrombocytopenia and/or neutropenia causing interruption of the 21-day course or persisting for more than 7 days after the last day of chemotherapy was seen at all dose levels, but was not dose-limiting. One patient treated at the 50-mg/m2 daily dose died of sepsis. At the 75-mg/m2 dose level, diarrhea was dose-limiting. Estimated plasma VP-16 concentrations were greater than 1 micrograms/mL for median periods of 9.4, 15.4, and 13.5 hours per day at daily doses of 50, 60, and 75 mg/m2, respectively. Responses were observed in seven of 14 patients who received at least one additional course of etoposide after a rest period of 7 days. There was one complete and two objective responses. Four patients were considered to have stable disease.

The intravenous preparation of VP-16 administered orally appears to be well tolerated by heavily pretreated pediatric patients. On the three-times daily, 21-day schedule, a daily dose of 75 mg/m2 exceeds the MTD, with diarrhea as the dose-limiting toxicity. The recommended dose for oral etoposide is 60 mg/m2/d administered every 8 hours.