title: Influence of P-glycoprotein on the disposition of fexofenadine and its enantiomers.
abstract: OBJECTIVE
  P-glycoprotein (P-gp) is responsible for the efflux of a broad variety of human and veterinary drugs. Canine P-gp polymorphisms alter drug disposition and toxicity, but their impact on the disposition of enantiomeric drugs is unknown. Using fexofenadine as a model compound, we developed and validated HPLC-fluorescence methods to determine the effect of P-gp on the disposition of fexofenadine and its enantiomers.
  
  
  METHODS
  A chiral CD-Ph column was used for the separation of (R) and (S)-fexofenadine. Determination of racemic fexofenadine was achieved on an XDB-CN column. Fexofenadine and its enantiomers were detected by fluorescence at the excitation wavelength of 220 nm and emission wavelength of 300 nm. These methods were used to measure concentrations of fexofenadine and its enantiomers in Collie plasma after oral administration.
  
  
  RESULTS
  This study demonstrates that P-gp prefers to transport (S)-fexofenadine, and P-gp deficiency causes the increase in both (R)-fexofenadine and (S)-fexofenadine in plasma. Racemic fexofenadine, (R)-fexofenadine and (S)-fexofenadine were increased in ABCB1-1Δ Collies (118.7, 72.0 and 48.3 ng/ml) compared to wild-type Collies (25.0, 16.5 and 7.7 ng/ml) at 1 h postadministration. The results demonstrate that the stereoselectivity of P-gp plays a key role in the disposition of fexofenadine enantiomers.
  
  
  CONCLUSIONS
  The information derived from this drug model will be used to determine whether additional safety or efficacy requirements are necessary for enantiomeric drugs that would be used in dogs or humans.
authors.affiliation: Division of Applied Veterinary Research, Office of Research, Center for Veterinary Medicine, U.S. Food and Drug Administration, Laurel, MD, USA.
authors.forename: Fei
authors.initials: F
authors.lastname: Li
authors.affiliation: Division of Applied Veterinary Research, Office of Research, Center for Veterinary Medicine, U.S. Food and Drug Administration, Laurel, MD, USA.
authors.forename: Karyn D
authors.initials: KD
authors.lastname: Howard
authors.affiliation: Division of Applied Veterinary Research, Office of Research, Center for Veterinary Medicine, U.S. Food and Drug Administration, Laurel, MD, USA.
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Myers
mesh_terms: D018435:ATP Binding Cassette Transporter, Subfamily B / Q000378:metabolism; D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000378:metabolism*; D000818:Animals; D002851:Chromatography, High Pressure Liquid / Q000379:methods; D004285:Dogs; D005453:Fluorescence; D013237:Stereoisomerism; D016593:Terfenadine / Q000031:analogs & derivatives* / Q000097:blood / Q000378:metabolism
chemical_list: C513055:ABCB1 protein, human; D018435:ATP Binding Cassette Transporter, Subfamily B; D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D016593:Terfenadine; C093230:fexofenadine
keywords: ABCB1-1Δ; Collies; enantiomer; fexofenadine; fluorescence