Kvet Forum
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Amitraz is a topical acaricide and insecticide widely used in most large animal species including cattle, sheep and goats. It is not labeled for use in horses and donkeys because they are easily poisoned when amitraz is applied to their skin or accidentally ingested.
PATHOGENESIS
Amitraz is a centrally acting α2 adrenergic agonist that also inhibits monoamine oxidase and prostaglandin synthesis. It is highly soluble and is rapidly absorbed through skin and mucous membranes.
Environmental temperature and the condition of the skin may influence absorption of the compound, clinical signs, and susceptibility of the animal.
CLINICAL FINDINGS
Clinical signs occur in horses within 12 to 48 hours and include: anorexia, depression, sedation, ataxia, incoordination, and large intestine impaction. Resolution of signs may take 7 to 8 days. Equine susceptibility to amitraz is likely caused by prolonged persistence in the body.
Salivation, depression, anorexia, ataxia, tremors, and coma are signs attributed to amitraz in other species.
TREATMENT
Decontamination with activated charcoal and a cathartic may be used in an ingestion if clinical signs have not yet occurred.
Residual topical amitraz should be removed from affected animals by bathing with soap and tepid water.
Further therapy is supportive and includes oral or intravenous fluids, analgesics, and treatment of the impaction colic.
The use of α2 adrenergic antagonists such as yohimbine and atipamezole has been suggested.