Intratracheal clenbuterol in the horse: its pharmacological efficacy and analytical detection

Abstract

Clenbuterol, a beta2 agonist/antagonist, is the only bronchodilator approved by the US Food and Drug Administration for use in horses. The Association of Racing Commissioners International classifies clenbuterol as a class 3 agent, and, as such, its identification in post-race samples may lead to sanctions. Anecdotal reports suggest that clenbuterol may have been administered by intratracheal (IT) injection to obtain beneficial effects and avoid post-race detection. The objectives of this study were (1) to measure the pharmacological efficacy of IT dose of clenbuterol and (2) to determine the analytical findings in urine in the presence and absence of furosemide. When administered intratracheally (90 microg/horse) to horses suffering from chronic obstructive pulmonary disease (COPD), clenbuterol had effects that were not significantly different from those of saline. In parallel experiments using a behavior chamber, no significant effects of IT clenbuterol on heart rate or spontaneous locomotor activity were observed. Clenbuterol concentrations in the urine were also measured after IT dose in the presence and absence of furosemide. Four horses were administered i.v. furosemide (5 mg/kg), and four horses were administered saline (5 mL). Two hours later, all horses were administrated clenbuterol (IT, 90 microg), and the furosemide-treated horses received a second dose of furosemide (2.5 mg/kg, i.v.). Three hours after clenbuterol dose (1 h after hypothetical 'post-time'), the mean specific gravity of urine samples from furosemide-treated horses was 1.024, well above the 1.010 concentration at which furosemide is considered to interfere with drug detection. There was no interference by furosemide with 'enhanced' ELISA screening of clenbuterol equivalents in extracted and concentrated samples. Similarly, furosemide had no effect on mass spectral identification or quantification of clenbuterol in these samples. These results suggest that the IT dose of clenbuterol (90 microg) is, in pharmacological terms, indistinguishable from the dose of saline, and that, using extracted samples, clenbuterol dose is readily detectable at 3 h after dosing. Furthermore, concomitant dose of furosemide does not interfere with detection or confirmation of clenbuterol.

Doping detection in animals: A review of analytical methodologies published from 1990 to 2019

“…Beta 2 agonists (β2‐agonists) are a group of compounds that binds to adrenoceptors on the smooth muscle cell surface, inducing relaxation of these muscles, hence being frequently used as bronchodilators. The main bronchodilators of clinical use include clenbuterol, ractopamine, salbutamol, cimaterol, formoterol, salmeterol, terbutaline, fenoterol, and mabuterol, and their therapeutic indications in horses cover noninfectious respiratory diseases, such as chronic obstructive pulmonary disease and inflammatory airway disease, and infectious diseases in which they act as a supportive medication, for example, acting as mucokinetic agents 248–252 . Besides therapeutic use, at higher doses and/or after long‐term use, β2‐agonists produce side effects inducing protein synthesis and lipolysis 252,253 .…”

“…The main bronchodilators of clinical use include clenbuterol, ractopamine, salbutamol, cimaterol, formoterol, salmeterol, terbutaline, fenoterol, and mabuterol, and their therapeutic indications in horses cover noninfectious respiratory diseases, such as chronic obstructive pulmonary disease and inflammatory airway disease, and infectious diseases in which they act as a supportive medication, for example, acting as mucokinetic agents. [248][249][250][251][252] Besides therapeutic use, at higher doses and/or after long-term use, β2-agonists produce side effects inducing protein synthesis and lipolysis. 252,253 Additionally, drugs such as clenbuterol also stimulate the cardiac and central nervous systems, which could result in positive effects on the performance of racing animals.…”