Pennsylvania Animal Diagnostic Laboratory System
Globe PADLS right arrow Conferences right arrow Spring 2001 right arrow 5. Elimination Of Clenbuterol  
Previous | Next

Pharmacokinetics, Tissue Distribution, and Elimination Of Clenbuterol In The Horse: Preliminary Study

L.R. Soma, C.E. Uboh, F. Guan, E.K. Birks, D. Teleis, J.A. Rudy, D. Tsang

University of Pennsylvania School of Veterinary Medicine, Department of Clinical Studies, New Bolton Center
and
PA Equine Toxicology and Research Laboratory, Department of Chemistry, West Chester University, West Chester, PA 19382

Initial pharmacokinetic studies following IV administration of clenbuterol (1.6 m/kg) indicated a median elimination half-life (t½beta) of 8.3 h (7.9-9.4), Area Under the Time Concentration Curve (AUC) of 15.0 hr*ng/ml (6.9-16.3), and a Zero Time Concentration (Ct0) of 1.31 ng/ml (0.54-1.38). One-compartment, IV bolus 1st order elimination model was fitted to the data from each horse. Only 50.8% of the total amount of clenbuterol administered to the horse was accounted for in the 36 h collection period.

The lung is the target organ in clenbuterol administration, and its effect as a bronchodilator is dependent on its concentrations in the lung and bronchial muscle. The action of Clenbuterol on the bronchial smooth muscle is dependent upon its uptake and subsequent elimination by bronchial smooth muscle. The slow clearance of clenbuterol from the horse suggests that clenbuterol is sequestered into body tissues from where it is slowly released into the circulation and urine for a prolonged period of time.

The questions to be answered are:

  1. how rapidly do the concentrations in the bronchial and lung tissues decline (the target tissues) in relationship to the concentrations of clenbuterol in other body tissue compartments, and
  2. how is it related to the plasma concentrations.

If bronchial muscle and lung concentrations decline rapidly following the withdrawal of clenbuterol, then the slow release is primarily due to other body tissues retaining high concentrations of clenbuterol. It is this apparent slow release from body tissues that may contribute to the low concentrations of clenbuterol detected in urine and plasma samples for a prolonged period of time following the withdrawal of clenbuterol. The greatest drawback with this therapeutic medication is that it is slowly cleared from body tissues in horses resulting in the drug being detected and confirmed in very low concentrations in urine and plasma samples for a prolonged period of time after its administration had been discontinued. It is unlikely, that these low plasma, urinary and possibly tissue concentrations of clenbuterol have any pharmacological effect capable of influencing the performance of the racing horse.

The specific aims of this study are:

  1. To determine the pharmacokinetic and disposition of clenbuterol following intravenous and oral administrations, and to determine its elimination pattern in urine.
  2. To determine the relationship between plasma and urinary concentrations of clenbuterol and those in pulmonary and body tissues and the clearance of the drug from these body tissues relative to plasma and urine.
  3. To determine the pharmacodynamics of clenbuterol in the horse

[ Previous | Next | PADLS Home | Conferences | Spring 2001 | Email ]

Last updated: 24-Jan-2002 10:14:10
Last validated (XHTML 1.1): 19-Dec-2002 13:25:26