title: Mechanism of intestinal absorption of ranitidine and ondansetron: transport across Caco-2 cell monolayers.
abstract: We have investigated the transport of ranitidine and ondansetron across the Caco-2 cell monolayers. The apparent permeability co-efficients (Papp) were unchanged throughout the concentration range studied, indicating a passive diffusion pathway across intestinal mucosa. No metabolism was observed for ranitidine and ondansetron during the incubation with Caco-2 cell monolayers. Papp values for ranitidine and ondansetron (bioavailability of 50 and approximately 100% in humans, respectively) were 1.03 +/- 0.17 x 10(-7) and 1.83 +/- 0.055 x 10(-5) cm/sec, respectively. The Papp value for ranitidine was increased by 15- to 20-fold in a calcium-free medium or in the transport medium containing EDTA, whereas no significant change occurred with ondansetron, indicating that paracellular passive diffusion is not rate determining for ondansetron. Uptake of ondansetron by Caco-2 cell monolayers was 20- and 5-fold higher than that of ranitidine when the uptake study was carried out under sink conditions and at steady state. These results suggest that ranitidine and ondansetron are transported across Caco-2 cell monolayers predominantly via paracellular and transcellular pathways, respectively.
authors.affiliation: Department of Drug Metabolism, Glaxo Inc., Research Triangle Park, North Carolina 27709.
authors.forename: L S
authors.initials: LS
authors.lastname: Gan
authors.forename: P H
authors.initials: PH
authors.lastname: Hsyu
authors.forename: J F
authors.initials: JF
authors.lastname: Pritchard
authors.forename: D
authors.initials: D
authors.lastname: Thakker
mesh_terms: D001682:Biological Availability; D001693:Biological Transport, Active; D002118:Calcium / Q000494:pharmacology; D002460:Cell Line; D003470:Culture Media; D004058:Diffusion; D006801:Humans; D007408:Intestinal Absorption; D017294:Ondansetron / Q000493:pharmacokinetics*; D010539:Permeability; D011899:Ranitidine / Q000493:pharmacokinetics*
chemical_list: D003470:Culture Media; D017294:Ondansetron; D011899:Ranitidine; D002118:Calcium