Jd. Harkins et al., Intratracheal clenbuterol in the horse: its pharmacological efficacy and analytical detection, J VET PHARM, 23(4), 2000, pp. 251-260
Citations number
11
Categorie Soggetti
Veterinary Medicine/Animal Health
Journal title
JOURNAL OF VETERINARY PHARMACOLOGY AND THERAPEUTICS
Clenbuterol, a beta2 agonist/antagonist, is the only bronchodilator approve
d 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 sa
nctions. Anecdotal reports suggest that clenbuterol may have been administe
red by intratracheal (IT) injection to obtain beneficial effects and avoid
post-race detection. The objectives of this study were (1) to measure the p
harmacological efficacy of IT dose of clenbuterol and (2) to determine the
analytical findings in urine in the presence and absence of furosemide. Whe
n administered intratracheally (90 mug/horse) to horses suffering from chro
nic 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 concentr
ations in the urine were also measured after IT dose in the presence and ab
sence of furosemide. Four horses were administered i.v. furosemide (5 mg/kg
), and four horses were administered saline (5 mL). Two hours later, all ho
rses were administrated clenbuterol (IT, 90 mug), and the furosemide-treate
d horses received a second dose of furosemide (2.5 mg/kg, i.v.). Three hour
s after clenbuterol dose (1 h after hypothetical 'post-time'), the mean spe
cific gravity of urine samples from furosemide-treated horses was 1.024, we
ll above the 1.010 concentration at which furosemide is considered to inter
fere with drug detection. There was no interference by furosemide with 'enh
anced' ELISA screening of clenbuterol equivalents in extracted and concentr
ated samples. Similarly, furosemide had no effect on mass spectral identifi
cation or quantification of clenbuterol in these samples. These results sug
gest that the IT dose of clenbuterol (90 mug) is, in pharmacological terms,
indistinguishable from the dose of saline, and that, using extracted sampl
es, clenbuterol dose is readily detectable at 3 h after dosing. Furthermore
, concomitant dose of furosemide does not interfere with detection or confi
rmation of clenbuterol.