Treatment and resolution of zilpaterol hydrochloride toxicity in aQuarterHorse gelding

Abstract

Summary Zilpaterol hydrochloride is a β‐2 agonist utilised as a repartitioning agent in cattle. In recent years, it has also been used illicitly among human athletes and body builders, and administered to racehorses. While there are numerous anecdotal reports of the effects of zilpaterol in horses, this is the first documented clinical case of equine zilpaterol toxicity. The horse presented with marked tachycardia, profuse sweating and generalised muscle fasciculations. Ultimately, treatment was initiated with propranolol and the horse made a complete recovery.

Review of proposed MRLs, safety evaluation of products obtained from animals treated with zilpaterol and evaluation of the effects of zilpaterol on animal health and welfare

“…Adverse effects in horses after the administration of zilpaterol are reported by Wagner et al. () and Hepworth‐Warren and Alcott (). Wagner et al.…”

“…AST, CK, lactate dehydrogenase). Lameness and reluctance to ambulate was also observed after 2–3 days (Hepworth‐Warren and Alcott, ). When stopping the zilpaterol administration, horses returned to a clinically normal state after 2–4 weeks.…”

“…Wagner et al. () did a kinetic study where horses were fed 0.17 mg/kg bw zilpaterol in 0.5 pounds (lb) of grain mix, while Hepworth‐Warren and Alcott () report a case of inadvertent zilpaterol toxicity in a horse that ingested approximately 200 times the recommended daily dose of zilpaterol for cattle. The results of both studies showed that the administration of zilpaterol to horses provoked sweating, muscle tremors and severe tachycardia and the alteration of some biochemical parameters (i.e.…”

Accidental zilpaterol toxicity, food for thought

“…The case report in this issue by Hepworth‐Warren and Alcott is a well‐documented case of zilpaterol intoxication in horses. I congratulate the authors (Hepworth‐Warren and Alcott ) for this effort. The case as a record of chemical toxicity is complete and of great interest.…”

“…This was an accidental overdose (Hepworth‐Warren and Alcott ). Interestingly, a historical comment indicated that the horse had received chronic monensin feeding ‘without harm’ according to the owner.…”