WHO Acute Hazard classification: Class II, moderately hazardous.

Mechanism of action of Amitraz

The acaricidal and inseticidal activity of amitraz is due to its antagonistic effect on octopamine receptors of the nerve cells in the brain. Parasites become hyperexcited, paralyzed and eventually die. This mode of action is different from those of synthetic pyrethroids, organophosphates and other ectoparasiticides.

Acute Toxicity and Tolerance of Amitraz

• LD50 acute, rats, p.o. 800 mg/kg
• LD50 acute, mice, p.o. >1600 mg/kg
• LD50 acute, dogs, p.o. 100 mg/kg
• LD50 acute, rats, dermal >1600 mg/kg
• LD50 acute, rabbits, dermal >200 mg/kg
• As a general rule, dogs and livestock tolerate amitraz very well.
• WARNING: amitraz is toxic to cats and horses! It is lethal for hamsters and very toxic for numerous rodents.

Toxic Symptoms caused by Amitraz Poisoning

• General symptoms
• Hyperglycemia (excessive sugar in the blood)
• Hypothermia (too low body temperature)
• Polyuria (excessive urination)
• Gastrointestinal symptoms
• Lack of appetite
• Vomit
• Abdominal pain
• Reduced gut motility
• Central Nervous System (CNS)
• Sedation (reduced irritability or agitation)
• Depression
• Tremor (uncoordinated trembling or shaking movements)
• Circulatory system
• Hypotension (low blood pressure)
• Bradycardia (too low heart rate) that can turn to tachycardia (too high heart rate) and hyperventilation (too rapid breathing).
• In cats a singly bath at 125 ppm (=mg/l) equivalent to 0,0125% can already cause transient lack of appetite. A single bath at 250 ppm (equivalent to 0.025% can cause sustained sedation, depression and anorexia.
• Symptoms can appear within less than one hour after exposure, but depend strongly on the formulation, the dose and the kind of contact (dermal, ingestion etc).
• As a general rule, young animals are more sensitive to overdosing and react stronger. 
• A frequent cause of intoxications of pets is off-label use of products for livestock or crop protection on pets. Since such products do not include use instructions for pets, massive overdosing is possible, and inert ingredients in such products may also be toxic for pets.

Amitraz Side Effects, Adverse Drug Reactions (ADRs) and Warnings

• Chihuahua dogs should not be treated with amitraz: they are particularly sensitive.
• It is advisable not to treat pregnant bitches with amitraz, since information on tolerance to amitraz by many dog breeds is still scarce.
• Amitraz should not be used in puppies younger than 3 months.
• Animals should not be treated with amitraz by very hot weather, or if they are exposed to a strong and persistent sun irradiation, or if they are stressed by too high temperatures.
• Amitraz can cause transient itching and slight allergic reactions such as urticaria (hives) and edema (swelling) after the first treatments.
• Transient sedation has been observed in dogs after an amitraz bath, lasting for up to 24 hours, (up to 72 hours in puppies).
• After dipping or spraying cattle with amitraz it is typical that a few animals, especially young or weaker ones lay down or fall to the ground and remain sleepy for a certain time. Normally they recover spontaneously or they can be sprayed with abundant water to accelerate recovery.
• Never use spot-ons for dogs in cats; never use spot-ons for large dogs in small dogs. It happens that some users want to save money buying large tablets or spot-ons for treating smaller dogs (or even cats!) twice or more times. The risk of overdosing is considerable, either due to erroneous calculations or to unskilled manipulation.
• Unless prescribed by a veterinary doctor, never use in dogs or cats products for livestock that are not explicitly approved for such use. There is a high risk of overdosing or of adverse drug reactions due to ingredients that are not tolerated by pets or are even toxic to them.

Antidote and Treatment of Amitraz Intoxication

• Atipamezole, 50 mcg/kg i.m. The effect is very fast but lasts only 2-4 hours. After this first treatment it may be necessary to administer Yohimbine (0.1 mg/kg p.o.) every 6 hours till complete recovery.
• Yohimbine 0.1 mg/kg i.v. is usually the best oprion. It displaces amitraz from the alpha2 receptors, which relieves bradycardia, hypotension, and sedation, and restores gut motility.
• In case of horse intoxication do not administer atropine, morphine or spasmolytic painkillers.
• After topical administration (dip, spray, spot-on) wash the animal with abundant cold water to remove product remains in the hair coat, taking care not to cause peripheral vasodilation.

Pharmacokinetics of Amitraz

• Dermal absorption of topically administered amitraz is quite low, less than 10% in dogs and pigs. However treated animals may ingest amitraz through licking and grooming.
• Absorption of ingested amitraz is rather low as well and most of it is quickly excreted unchanged through the feces.
• Absorbed amitraz is vastly broken down to metabolites in the liver. This occurs rather fast in ruminants, pigs and dogs, but much slower in horses, which may explain why they do not tolerate amitraz.
• Excretion of absorbed amitraz is achieved through the kidneys: 24 hours after treatment >60% of the administered dose is already excreted.

Environmental Toxicity of Amitraz

• Amitraz is slightly toxic to birds but can negatively affect their reproduction.
• Amitraz is moderately toxic to fish.
• Amitraz is rather safe for bees.
• Half-life in soil is <24 hours. Amitraz breaks down quickly in the soil, particularly in well-oxygenated and acid soils.
• Amitraz does not bioaccumulate.
• Correct use on dogs and livestock is unlikely to cause environmental pollution.
• Disposal of large amounts of old dip wash must be carried out following label instructions.

Additional information

Click here for a list and overview of all safety summaries of antiparasitic active ingredients in this site.

• Amitraz belongs to the chemical class of the amidines (also called formamidines). 
• Amitraz is not used in human medicines.
  
• Amitraz is used in crop pesticides.
• Amitraz is not used in public or domestic hygiene as a biocide.
• Click here for General safety of antiparasitics for domestic animals.
• Click here for General safety of antiparasitics for humans.
• Click here for General safety of antiparasitics for the environment.
• Click here for technical and commercial information on amitraz.