title: Pharmacokinetics and disposition of clenbuterol in the horse.
abstract: The pharmacokinetics of clenbuterol (CLB) following a single intravenous (i.v.) and oral (p.o.) administration twice daily for 7 days were investigated in thoroughbred horses. The plasma concentrations of CLB following i.v. administration declined mono-exponentially with a median elimination half-life (t(1/2k)) of 9.2 h, area under the time-concentration curve (AUC) of 12.4 ng.h/mL, and a zero-time concentration of 1.04 ng/mL. Volume of distribution (V(d)) was 1616.0 mL/kg and plasma clearance (Cl) was 120.0 mL/h/kg. The terminal portion of the plasma curve following multiple p.o. administrations also declined mono-exponentially with a median elimination half-life (t(1/2k)) of 12.9 h, a Cl of 94.0 mL/h/kg and V(d) of 1574.7 mL/kg. Following the last p.o. administration the baseline plasma concentration was 537.5 +/- 268.4 and increased to 1302.6 +/- 925.0 pg/mL at 0.25 h, and declined to 18.9 +/- 7.4 pg/mL at 96 h. CLB was still quantifiable in urine at 288 h following the last administration (210.0 +/- 110 pg/mL). The difference between plasma and urinary concentrations of CLB was 100-fold irrespective of the route of administration. This 100-fold urine/plasma difference should be considered when the presence of CLB in urine is reported by equine forensic laboratories.
authors.affiliation: School of Veterinary Medicine, University of Pennsylvania, New Bolton Center Campus, West Street Road, Kennett Square, PA 19348, USA. soma@mail.vet.upenn.edu
authors.forename: L R
authors.initials: LR
authors.lastname: Soma
authors.forename: C E
authors.initials: CE
authors.lastname: Uboh
authors.forename: F
authors.initials: F
authors.lastname: Guan
authors.forename: P
authors.initials: P
authors.lastname: Moate
authors.forename: Y
authors.initials: Y
authors.lastname: Luo
authors.forename: D
authors.initials: D
authors.lastname: Teleis
authors.forename: R
authors.initials: R
authors.lastname: Li
authors.forename: E K
authors.initials: EK
authors.lastname: Birks
authors.forename: J A
authors.initials: JA
authors.lastname: Rudy
authors.forename: D S
authors.initials: DS
authors.lastname: Tsang
mesh_terms: D000284:Administration, Oral; D000818:Animals; D019540:Area Under Curve; D001993:Bronchodilator Agents / Q000008:administration & dosage / Q000097:blood / Q000493:pharmacokinetics*; D002976:Clenbuterol / Q000008:administration & dosage / Q000097:blood / Q000493:pharmacokinetics*; D005260:Female; D006207:Half-Life; D006736:Horses; D007275:Injections, Intravenous; D007408:Intestinal Absorption; D008657:Metabolic Clearance Rate; D014018:Tissue Distribution
chemical_list: D001993:Bronchodilator Agents; D002976:Clenbuterol