title: The pharmacokinetics of etretinate and its metabolites in the dog.
abstract: The pharmacokinetics and disposition of etretinate (ET) and its metabolites, etretin (ETA) and isoetretin (c-ETA), were studied in the dog. Administration of ET, ETA, and c-ETA by several routes of administration allowed the use of a physiologically based model to assess the relative contributions of absorption and presystemic metabolism to the oral bioavailability of these compounds. The large Vdss (214 +/- 228 liters/kg) of ET and terminal half-life of greater than 300 hr indicated the wide distribution and prolonged storage of ET in the tissues. After a dose of ET, its two metabolites, ETA and c-ETA, were also detectable in the plasma. The oral bioavailability of ET in the dog was 52.5% with 95.4% of the dose available for absorption from the gut lumen. Of the ET that was absorbed from the gut lumen, 26.4% and 25.5% was removed by the gut wall and liver, respectively. ETA was found to be a formation rate-limited metabolite of ET. Although the oral bioavailability of ETA could not be determined because its administration was not possible by the iv route, it appeared that only 16% of an orally administered dose entered the portal circulation from the gut. c-ETA was detected after administration of either ET or ETA. ETA and c-ETA were shown to be interconvertible metabolites, but the equilibrium of the conversion between c-ETA and ETA favored the formation of ETA. The oral bioavailability of c-ETA was 42.4%, but the liver showed little metabolic activity toward c-ETA.(ABSTRACT TRUNCATED AT 250 WORDS)
authors.affiliation: College of Pharmacy, University of Minnesota, Minneapolis 55455.
authors.forename: P
authors.initials: P
authors.lastname: Thongnopnua
authors.forename: J W
authors.initials: JW
authors.lastname: Massarella
authors.forename: C L
authors.initials: CL
authors.lastname: Zimmerman
mesh_terms: D017255:Acitretin; D000818:Animals; D001682:Biological Availability; D002404:Catheterization; D004285:Dogs; D004305:Dose-Response Relationship, Drug; D005050:Etretinate / Q000008:administration & dosage / Q000097:blood / Q000493:pharmacokinetics*; D007275:Injections, Intravenous; D007408:Intestinal Absorption; D007413:Intestinal Mucosa / Q000378:metabolism*; D007422:Intestines / Q000187:drug effects; D008297:Male; D008954:Models, Biological; D014212:Tretinoin / Q000008:administration & dosage / Q000031:analogs & derivatives / Q000097:blood / Q000493:pharmacokinetics
chemical_list: D014212:Tretinoin; D005050:Etretinate; D017255:Acitretin