BIOAVAILABILITY OF LOW-DOSE ORAL ETOPOSIDE

Purpose: To determine the bioavailability of oral etoposide capsules administered at doses of 100 mg and 400 mg. Patients and Methods: The bioavailability of oral etoposide was determined by measuring the area under the etoposide plasma concentration versus time curve (AUC) following intravenous (IV) etoposide administration and comparing that value to the AUC achieved following an oral dose administered 1 day later to the same patient. The bioavailability of a 100-mg oral dose of etoposide was measured on 16 occasions in 11 patients. The bioavailability of a 400-mg dose was determined on 12 occasions in six patients. Results: The mean (± SD) bioavailability following a 100-mg dose of oral etoposide was 76% ± 22%, which was significantly greater (P < .01) than the mean bioavailability of 48% ± 18% following a 400-mg oral dose. The coefficient of variation in oral etoposide bioavailability was significant: 29% with a 100-mg oral dose and 37% with a 400-mg dose. Conclusion: Bioavailability of a 100-mg oral etoposide dose is greater than suggested in the package insert from Bristol Laboratories (Evansville, IN). Comparable oral etoposide doses are not uniformly twice that of an IV dose, as suggested by the package insert, but will depend on the final oral dose administered. Bioavailability is better at lower oral etoposide doses. This study confirms the wide interpatient and intrapatient variability in oral etoposide bioavailability.