title: Sensitivity and proportionality assessment of metabolites from microdose to high dose in rats using LC-MS/MS.
abstract: BACKGROUND
  The objective of this study was to evaluate the sensitivity requirement for LC-MS/MS as an analytical tool to characterize metabolites in plasma and urine at microdoses in rats and to investigate proportionality of metabolite exposure from a microdose of 1.67 µg/kg to a high dose of 5000 µg/kg for atorvastatin, ofloxacin, omeprazole and tamoxifen.
  
  
  RESULTS
  Only the glucuronide metabolite of ofloxacin, the hydroxylation metabolite of omeprazole and the hydration metabolite of tamoxifen were characterized in rat plasma at microdose by LC-MS/MS. The exposure of detected metabolites of omeprazole and tamoxifen appeared to increase in a nonproportional manner with increasing doses. Exposure of ortho- and para-hydroxyatorvastatin, but not atorvastatin and lactone, increased proportionally with increasing doses.
  
  
  CONCLUSIONS
  LC-MS/MS has demonstrated its usefulness for detecting and characterizing the major metabolites in plasma and urine at microdosing levels in rats. The exposure of metabolites at microdose could not simply be used to predict their exposure at higher doses.
authors.affiliation: RD2-2B, Department of Drug Safety Evaluation, Allergan, 2525 Dupont Drive, Irvine, CA 92612, USA. ni_jinsong@ allergan.com
authors.forename: Jinsong
authors.initials: J
authors.lastname: Ni
authors.forename: Hui
authors.initials: H
authors.lastname: Ouyang
authors.forename: Carmai
authors.initials: C
authors.lastname: Seto
authors.forename: Takeo
authors.initials: T
authors.lastname: Sakuma
authors.forename: Robert
authors.initials: R
authors.lastname: Ellis
authors.forename: Josh
authors.initials: J
authors.lastname: Rowe
authors.forename: Andrew
authors.initials: A
authors.lastname: Acheampong
authors.forename: Devin
authors.initials: D
authors.lastname: Welty
authors.forename: Gabriella
authors.initials: G
authors.lastname: Szekely-Klepser
mesh_terms: D000818:Animals; D000069059:Atorvastatin; D002853:Chromatography, Liquid / Q000379:methods*; D004305:Dose-Response Relationship, Drug; D006538:Heptanoic Acids / Q000008:administration & dosage / Q000378:metabolism / Q000493:pharmacokinetics / Q000494:pharmacology; D008297:Male; D055442:Metabolome / Q000187:drug effects*; D015242:Ofloxacin / Q000008:administration & dosage / Q000378:metabolism / Q000493:pharmacokinetics / Q000494:pharmacology; D009853:Omeprazole / Q000008:administration & dosage / Q000378:metabolism / Q000493:pharmacokinetics / Q000494:pharmacology; D010599:Pharmacokinetics; D011758:Pyrroles / Q000008:administration & dosage / Q000378:metabolism / Q000493:pharmacokinetics / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D013629:Tamoxifen / Q000008:administration & dosage / Q000378:metabolism / Q000493:pharmacokinetics / Q000494:pharmacology; D053719:Tandem Mass Spectrometry / Q000379:methods*
chemical_list: D006538:Heptanoic Acids; D011758:Pyrroles; D013629:Tamoxifen; D000069059:Atorvastatin; D015242:Ofloxacin; D009853:Omeprazole