A randomized trial of two etoposide schedules in small-cell lung cancer: the influence of pharmacokinetics on efficacy and toxicity.

PURPOSE Etoposide is a schedule-dependent drug, as demonstrated by the superiority of 5 consecutive daily infusions over a continuous 24-hour infusion in patients with small-cell lung cancer. A randomized trial has therefore been conducted to compare an extended 8-day regimen with the 5-day schedule. PATIENTS AND METHODS Ninety-four patients with small-cell lung cancer (35 limited disease, 59 extensive disease) were randomized to receive single-agent etoposide 500 mg/m2, either as 5 daily 2-hour infusions of 100 mg/m2 or as 8 daily 75-minute infusions of 62.5 mg/m2, both repeated every 3 weeks for six cycles. Single-agent carboplatin was administered at relapse in both arms of the study. Patients were stratified at randomization according to extent of disease and Karnofsky performance status (KPS). RESULTS The overall response rate was 81% in the 5-day arm and 87% in the 8-day arm, with median survival durations of 7.1 and 9.4 months, respectively (no significant differences). The time over which plasma etoposide exceeded low plasma concentrations was significantly longer in patients who responded compared with patients who did not respond. This was most significant for time at concentrations greater than 1, 1.5, and 2 micrograms/mL. Hematologic toxicity was significantly worse in the 5-day arm of the study (cycle no. 1 nadir neutrophil count, 0.8 x 10(9)/L v 1.7 x 10(9)/L). Stepwise regression analysis found duration of exposure to plasma etoposide greater than 3 micrograms/mL to be predictive of nadir neutrophil count and duration of exposure to plasma etoposide greater than 2 micrograms/mL to be predictive of nadir WBC count. CONCLUSION The 5-day and 8-day regimens had equivalent activity in small-cell lung cancer. A pharmacokinetic association between concentrations of etoposide and response and toxicity was found. Antitumor activity was associated with the maintenance of lower levels of etoposide than found to be associated with hematologic toxicity. This supports the hypothesis that the schedule of etoposide administration may affect efficacy and toxicity, and that prolonged exposure to low concentrations of etoposide may improve the therapeutic ratio for this drug.