Amitraz

Formamidine acaricide/insecticide Alpha-2 adrenergic agonist / monoamine oxidase inhibitor

Dosage & Administration Guidelines

Species Route Dose Frequency Duration & Clinical Notes
Dog Topical (dip) 250 ppm (0.025%) solution Every 7-14 days Duration: Until 2 consecutive negative skin scrapings (usually 4-8 weeks)
Notes: For generalized demodicosis. Clip long hair, bathe with benzoyl peroxide shampoo, rinse, and apply dip. Allow to air dry. Do not rinse after application. Use in well-ventilated area.
Dog Topical (spot-on) Not approved; use dip only — Spot-on formulations are not available for dogs.
Horse Topical (sponge or spray) 0.025% solution (250 ppm) Every 7 days Duration: 2-4 treatments
Notes: For mange. Apply to affected areas. Do not use on debilitated animals.
Cattle Topical (spray or dip) 0.025% solution (250 ppm) Single application, may repeat in 14 days Duration: As needed
Notes: For tick control and mange. Do not treat calves under 3 months of age.
Small Ruminants (Sheep/Goats) Topical (spray or dip) 0.025% solution (250 ppm) Single application, may repeat in 14 days Duration: As needed
Notes: For tick and mite control. Observe withdrawal times.
Rabbit Topical (dip or sponge) 0.025% solution (250 ppm) Every 7 days Duration: 2-4 treatments
Notes: For ear mites and fur mites. Use with caution; monitor for sedation.
Exotic (Guinea pig, Rat, Hamster) Topical (dip or sponge) 0.025% solution (250 ppm) Every 7 days Duration: 2-4 treatments
Notes: Off-label use. Use extreme caution due to small size and risk of toxicity.

Clinical Indications & Species Uses

General Indications
  • Ectoparasiticidal for ticks, mites, and lice in various species
Dog (Canine)
  • Treatment of generalized demodicosis (Demodex canis)
  • Treatment of localized demodicosis
  • Treatment of sarcoptic mange (Sarcoptes scabiei)
  • Treatment of cheyletiellosis
  • Control of ticks (e.g., Rhipicephalus sanguineus, Dermacentor variabilis)
Horse (Equine)
  • Treatment of sarcoptic mange
  • Treatment of psoroptic mange
  • Treatment of chorioptic mange
Cattle (Bovine)
  • Control of ticks (e.g., Boophilus, Rhipicephalus)
  • Treatment of sarcoptic mange
  • Treatment of psoroptic mange
  • Treatment of chorioptic mange
  • Control of lice (Linognathus, Haematopinus)
Small Ruminants (Sheep / Goat)
  • Control of ticks
  • Treatment of sarcoptic mange
  • Treatment of psoroptic mange
Rabbit & Small Mammals
  • Treatment of ear mites (Psoroptes cuniculi)
  • Treatment of fur mites (Cheyletiella parasitovorax)
Exotic & Other Species
  • Treatment of mites in guinea pigs (off-label)
  • Treatment of mites in rats (off-label)
  • Treatment of mites in hamsters (off-label)

Pharmacology & Mechanism of Action

Drug Class: Formamidine acaricide/insecticide | Pharmacological Group: Alpha-2 adrenergic agonist / monoamine oxidase inhibitor

Mechanism of Action: Amitraz is a formamidine compound that acts as an agonist at alpha-2 adrenergic receptors in both invertebrates and mammals. In target arthropods (ticks, mites, lice), it stimulates the release of biogenic amines (e.g., octopamine) and inhibits monoamine oxidase, leading to overexcitation of the nervous system, paralysis, and death. In mammals, it primarily stimulates central alpha-2 adrenergic receptors, resulting in sedation, bradycardia, and decreased central sympathetic outflow. It also has local anesthetic and antipruritic effects.

Pharmacodynamics: Amitraz exhibits acaricidal and insecticidal activity against a broad range of ectoparasites, including ticks (e.g., Rhipicephalus, Dermacentor, Ixodes), mites (Sarcoptes, Demodex, Otodectes), and lice. Its effects are dose-dependent; at therapeutic doses it controls parasites, while at higher doses it can cause significant CNS depression and cardiovascular effects in mammals. It also has a repellent effect against some ticks. In dogs, it reduces pruritus associated with demodicosis.

⚡ Pharmacokinetics Summary

Absorption: Amitraz is well absorbed through the skin after topical application, with systemic absorption varying by formulation and species. In dogs, dermal absorption is significant, and peak plasma concentrations occur within hours. Oral absorption is rapid and complete.
Distribution: Amitraz is widely distributed in tissues, with high concentrations in the liver, kidneys, and skin. It crosses the blood-brain barrier, which contributes to its central effects. It is also distributed to milk in lactating animals.
Metabolism: Amitraz is extensively metabolized in the liver, primarily to 2,4-dimethylaniline (DMA) and other metabolites. Metabolism involves hydrolysis and oxidation. The metabolites are excreted in urine and feces.
Excretion: Amitraz and its metabolites are excreted primarily in urine (approximately 70-80%) and feces (20-30%). In lactating animals, small amounts are excreted in milk.
Half-Life: Dog: approximately 24 hours (after topical application); Cattle: approximately 6-12 hours (after topical application); Rat: 2-4 hours (IV).
Bioavailability: Topical: variable, but significant systemic absorption occurs (estimated 30-50% in dogs). Oral: high (approximately 90%).
Protein Binding: Amitraz is moderately protein-bound (approximately 60-70%) in plasma.

Available Formulations & Strengths

Concentrate for dipping solution 12.5% (125 mg/mL) or 19.9% (199 mg/mL) (Topical)
Ready-to-use dip solution 0.025% (250 ppm) (Topical)
Collar (for dogs) 9% (e.g., Preventic collar) (Topical)

Contraindications & Clinical Warnings

Contraindications:
  • Hypersensitivity to amitraz or other formamidines
  • Do not use in cats (highly toxic)
  • Do not use in dogs that are pregnant, debilitated, or have a history of seizures
  • Do not use in animals with diabetes mellitus (may cause hyperglycemia)
  • Do not use in young animals (e.g., puppies under 3 months, calves under 3 months)
  • Do not use in animals with respiratory disease (may cause respiratory depression)
  • Do not use concurrently with other alpha-2 agonists (e.g., xylazine, detomidine) or MAO inhibitors
Warnings & Clinical Precautions:
  • Use with caution in animals with cardiovascular disease, hepatic or renal impairment
  • Avoid contact with eyes and mucous membranes; wear protective gloves and clothing when handling
  • Do not apply to broken or abraded skin
  • Do not allow animal to lick the treated area until dry
  • Use in well-ventilated areas to avoid inhalation
  • In dogs, transient sedation, bradycardia, and hyperglycemia may occur; monitor closely
  • Do not use in animals that are stressed or overheated
  • Do not use in animals that have been treated with other ectoparasiticides within 7 days
  • In food animals, observe withdrawal times
  • Keep out of reach of children and other animals

Adverse Effects & Reactions

Common:

  • Sedation
  • Lethargy
  • Bradycardia
  • Hyperglycemia
  • Vomiting
  • Diarrhea
  • Pruritus (transient)
  • Local skin irritation

Serious / Severe:

  • Respiratory depression
  • Hypotension
  • Seizures
  • Coma
  • Death (especially in cats)
  • Prolonged sedation
  • Hypothermia

Rare:

  • Allergic reactions
  • Hepatotoxicity
  • Pancreatitis
  • Bone marrow suppression

Key Drug Interactions

Interacting Drug / Class Clinical Effect & Mechanism Severity
Alpha-2 adrenergic agonists (xylazine, detomidine, medetomidine) Additive CNS depression, bradycardia, and hypotension High
MAO inhibitors (e.g., selegiline) Additive monoamine oxidase inhibition, increased risk of serotonin syndrome High
Other ectoparasiticides (e.g., organophosphates, pyrethroids) Additive toxicity, increased risk of adverse effects Moderate
Anticholinergics (e.g., atropine) May antagonize some effects of amitraz; use with caution Moderate
Corticosteroids May mask signs of toxicity or alter immune response Mild

Overdose & Toxicity Management

Signs of Toxicity:

  • Severe sedation
  • Coma
  • Respiratory depression
  • Bradycardia
  • Hypotension
  • Hypothermia
  • Hyperglycemia
  • Mydriasis
  • Vomiting
  • Seizures (in severe cases)

Emergency Treatment Protocol: There is no specific antidote. Treatment is symptomatic and supportive. Administer oxygen and provide respiratory support. Administer IV fluids for hypotension. Atropine may be used to treat bradycardia (0.02-0.04 mg/kg IV). Yohimbine (alpha-2 antagonist) has been used to reverse CNS depression in dogs (0.1 mg/kg IV). Monitor blood glucose and treat hyperglycemia if necessary. Control seizures with diazepam or barbiturates. In cases of dermal exposure, wash the animal thoroughly with mild soap and water. Induce vomiting if recent oral ingestion and animal is conscious.

Food Animal Withdrawal Times

🥩 Meat: 7 days🥛 Milk: 4 days

Withdrawal times vary by country and formulation. In the US, for cattle, meat withdrawal is 7 days and milk withdrawal is 4 days. For sheep and goats, meat withdrawal is 7 days and milk withdrawal is 4 days. Not approved for poultry or egg-producing birds. Always follow label instructions and local regulations.

Storage, Handling & Regulatory Information

Storage Temperature: Store at room temperature (15-30°C / 59-86°F)

Handling & Special Conditions: Keep container tightly closed. Protect from freezing. Store away from food and feed. Keep out of reach of children.

Dispensing Status: Over-The-Counter (OTC)

Approval Status: FDA-approved for use in dogs (for demodicosis and tick control) and cattle (for tick and mange control). Also approved for horses in some countries. Not approved for cats.

Extra-Label (Off-Label) Use: In the US, amitraz is available as an over-the-counter (OTC) product for dogs and cattle. Extra-label use in other species (e.g., rabbits, exotic pets) is permitted under AMDUCA with a valid veterinarian-client-patient relationship. However, extra-label use in food animals requires careful attention to withdrawal times and may require a veterinary feed directive or prescription.

Clinical Pearls & Practice Notes

💡 Clinical Insights: Amitraz is a valuable ectoparasiticide, particularly for generalized demodicosis in dogs, where it is often the treatment of choice. It is also used for tick control in cattle and horses. However, its use requires careful handling and monitoring due to its potential for systemic toxicity, especially in small animals and cats. In dogs, sedation and bradycardia are common but usually transient; yohimbine can be used to reverse these effects if severe. For demodicosis, treatment should be continued until two consecutive negative skin scrapings are obtained, which may take several months. In food animals, strict adherence to withdrawal times is essential. Due to its alpha-2 agonist activity, amitraz should not be used concurrently with other alpha-2 agonists or MAO inhibitors. Always wear protective gloves when handling the concentrate and ensure adequate ventilation. In cats, amitraz is contraindicated due to a high risk of fatal toxicity. For off-label use in exotic pets, extreme caution and dose reduction are advised.

References & Literature

  • 📚 Plumb's Veterinary Drug Handbook
  • 📚 Papich Veterinary Pharmacology and Therapeutics
  • 📚 Compendium of Veterinary Products (CVP)