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.