title: Microdosing assessment to evaluate pharmacokinetics and drug metabolism in rats using liquid chromatography-tandem mass spectrometry.
abstract: OBJECTIVE
  To evaluate the sensitivity requirement for LC-MS/MS as an analytical tool to support human microdosing study with sub-pharmacological dose, investigate proportionality of pharmacokinetics from the microdose to therapeutic human equivalent doses in rats and characterize circulating metabolites in rats administered with the microdose.
  
  
  METHODS
  Five drugs of antipyrine, metoprolol, carbamazepine, digoxin and atenolol were administered orally to male Sprague-Dawley rats at 0.167, 1.67, 16.7, 167 and 1,670 microg/kg doses. Plasma samples were extracted using either solid phase extraction or liquid-liquid extraction, and analyzed using LC-MS/MS.
  
  
  RESULTS
  Using 100 microl of plasma sample, the lower limit of quantitation for antipyrine (10 pg/ml), carbamazepine (1 pg/ml), metoprolol (5 pg/ml), atenolol (20 pg/ml), and digoxin (5 pg/ml) were achieved using an API 5000. Proportional pharmacokinetics were observed from 0.167 microg/kg to 1,670 microg/kg for antipyrine and carbamazepine and from 1.67 to 1,670 microg/kg for atenolol and digoxin, while metoprolol exhibited a non-proportional pharmacokinetics relationship. Several metabolites of carbamazepine were characterized in plasma from rats dosed at 1.67 mug/kg using LC-MS/MS.
  
  
  CONCLUSIONS
  This study has shown the promise of sensitive LC-MS/MS method to support microdose pharmacokinetics and drug metabolism studies in human.
authors.affiliation: Department of Drug Safety Evaluation, Allergan, 2525 Dupont Drive, Irvine, California 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: Mauro
authors.initials: M
authors.lastname: Aiello
authors.forename: Carmai
authors.initials: C
authors.lastname: Seto
authors.forename: Lisa
authors.initials: L
authors.lastname: Borbridge
authors.forename: Takeo
authors.initials: T
authors.lastname: Sakuma
authors.forename: Robert
authors.initials: R
authors.lastname: Ellis
authors.forename: Devin
authors.initials: D
authors.lastname: Welty
authors.forename: Andrew
authors.initials: A
authors.lastname: Acheampong
mesh_terms: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000378:metabolism; D000818:Animals; D001682:Biological Availability; D001702:Biopharmaceutics; D002138:Calibration; D055598:Chemical Phenomena; D002627:Chemistry, Physical; D002853:Chromatography, Liquid; D066298:In Vitro Techniques; D007202:Indicators and Reagents; D008297:Male; D008862:Microsomes, Liver / Q000378:metabolism; D009249:NADP / Q000378:metabolism; D004364:Pharmaceutical Preparations / Q000378:metabolism*; D010599:Pharmacokinetics; D011786:Quality Control; D051381:Rats; D017207:Rats, Sprague-Dawley; D012015:Reference Standards; D021241:Spectrometry, Mass, Electrospray Ionization; D053719:Tandem Mass Spectrometry
chemical_list: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D007202:Indicators and Reagents; D004364:Pharmaceutical Preparations; D009249:NADP