title: Steady-state bioavailability and day-to-day variability of a multiple-unit (CR/ZOK) and a single-unit (OROS) delivery system of metoprolol after once-daily dosing.
abstract: Steady-state bioavailability and day-to-day variability of plasma levels were evaluated in 18 healthy male subjects in a crossover study of multiple once-daily administration of two novel oral drug delivery systems of metoprolol and an immediate-release tablet (100 mg metoprolol tartrate). Data were collected over two consecutive 24-hr dosing intervals on treatment days 6 and 7. The two extended-release formulations investigated were metoprolol CR/ZOK (95 mg metoprolol succinate), a multiple-unit system consisting of several hundred membrane-coated delivery units, and metoprolol OROS (95 mg metoprolol fumarate), a single-unit osmotic delivery system. The extended drug release and absorption observed after administration of metoprolol CR/ZOK and metoprolol OROS resulted in similar steady-state plasma concentrations after once-daily dosing. Compared to the immediate-release tablet, they produced considerably lower plasma peaks, three- to fourfold higher trough concentrations, 8-9 hr longer mean residence times, and 20% lower relative bioavailability. Moreover, the two once-daily metoprolol products were found bioequivalent in Cmax and AUC based on 90% confidence intervals for the mean ratio CR/OROS. Repeated plasma concentration measurements on two consecutive 24-hr periods suggested that all three metoprolol treatments produced reproducible and consistent plasma concentrations from day to day at steady state. Assessment of day-to-day variability, however, resulted in significantly lower variation in AUC for the multiple-unit CR/ZOK formulation compared to the single-unit OROS tablet. These results imply that there may be formulation-related differences in the in vivo behavior of the two products despite their being bioequivalent in extent and rate of absorption.
authors.affiliation: Department of Biopharmaceutics and Project Coordination, Astra Hässle AB, Mölndal, Sweden.
authors.forename: A
authors.initials: A
authors.lastname: Sandberg
authors.forename: B
authors.initials: B
authors.lastname: Abrahamsson
authors.forename: A
authors.initials: A
authors.lastname: Svenheden
authors.forename: B
authors.initials: B
authors.lastname: Olofsson
authors.forename: R
authors.initials: R
authors.lastname: Bergstrand
mesh_terms: D000328:Adult; D001682:Biological Availability; D016503:Drug Delivery Systems; D006207:Half-Life; D006801:Humans; D008297:Male; D008790:Metoprolol / Q000008:administration & dosage / Q000493:pharmacokinetics*
chemical_list: D008790:Metoprolol