Chapter 29 Amitraz
Amitraz is a formamidine antiparasitic agent. Amitraz dips are primarily used to treat demodicosis in dogs, but are also used for external parasites in several species, including cattle, rabbits, goats, and cats.1 Amitraz is also found in tick control collars for dogs and contains 9.0% amitraz (Box 29-1). Collars weigh 27.5 g, and there are 2500 mg of amitraz per collar (Preventic package label insert).
The oral median lethal dose (LD50) of amitraz in dogs is 250 mg/kg [Registry of Toxic Effects of Chemical Substances (RTECS)]. According to a study, beagles receiving 4 mg/kg PO daily for 90 days exhibited signs of transient ataxia, CNS depression, hyperglycemia, decreased pulse rates, and lowered body temperature.1 In another study, dogs that were given 100 mg of amitraz/kg at three dose rates showed clinical signs of sedation, bradycardia, polyuria, hypothermia, and hyperglycemia.3
Amitraz is rapidly absorbed orally. Following doses of 100 mg/kg in dogs, peak plasma concentrations were observed after 5 hours with an elimination half-life of approximately 24 hours.3
MECHANISM OF TOXICITY
The exact pharmacological action of amitraz is not completely known; however, it does possess α2-adrenergic activity.1 Amitraz can cause a notable increase in plasma glucose levels, possibly from inhibiting insulin release through α2-adrenergic activity.1,4