Pharmacokinetics and disposition of clenbuterol in the horse.
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.
Soma
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LR
School of Veterinary Medicine, University of Pennsylvania, New Bolton Center Campus, West Street Road, Kennett Square, PA 19348, USA. soma@mail.vet.upenn.edu
Uboh
C E
CE
Guan
F
F
Moate
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P
Luo
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Y
Teleis
D
D
Li
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Birks
E K
EK
Rudy
J A
JA
Tsang
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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
D001993:Bronchodilator Agents; D002976:Clenbuterol