Pharmacodynamics of prolonged oral etoposide in patients with advanced non-small-cell lung cancer

This study was undertaken to investigate the pharmacodynamic relationship between etoposide drug levels on 21-day oral treatment courses and hematologic toxicities in patients with advanced non-small-cell lung cancer (NSCLC).

Thirty-two patients with stage IIIB or IV NSCLC were treated with oral etoposide 50 mg/m2/d for 21 consecutive days in combination with cisplatin 100 mg/m2 on day 1. Treatment was repeated every 28 days for up to six courses. Patients had not received previous chemotherapy and had a performance status of 0 to 2. Patients were monitored weekly while on treatment for compliance with oral etoposide and toxicity, including complete blood cell counts, and a blood sample before the daily etoposide dose (drug trough levels). Etoposide concentrations were measured in the plasma by high-performance liquid chromatography (HPLC).

Three patients achieved a complete response (CR) and 10 patients a partial response for an objective response rate of 41% (95% confidence interval, 24% to 58%). The median survival was 4 months (range, 1 to 23). Neutropenia was dose-limiting, and two patients died of neutropenic sepsis. Pharmacodynamic correlations for drug concentrations and hematologic toxicities were available for 27 patients and a total of 76 treatment courses, and correlations were significant for graded hematologic toxicity and nadir counts of leukocytes, neutrophils, hemoglobin, and platelets. The grade of infection (77 courses) was also related to drug levels. Using data from 27 initial courses, a pharmacodynamic model was developed to estimate the nadir leukocyte or neutrophil count (WBCn, ANCn) based on the pretreatment count (WBCp, ANCp) and the etoposide concentration (Ec) as follows: WBCn = 0.35 (1 + WBCp x e-1.12 x Ec) and ANCn = 0.32 (1 + ANCp x e-2.47 x Ec).

Etoposide concentrations are related to the resulting hematologic toxicities. It is possible to predict nadir counts in the first course by a pharmacodynamic model. The above equations need to be validated prospectively and may be useful in future studies of prolonged oral etoposide.