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Standards of Care June 2009 (Vol 11, No 5)

Amitraz Toxicity

by Chiara Valtolina, DVM, MRCVS, Sophie Adamantos, BVSc, CVA, DACVECC, MRCVS

    CETEST This course is approved for 1.0 CE credits

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    Introduction

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    Amitraz (N'-2,4-(dimethylphenyl)-N-(((2,4-dimethylphenyl)imino)methyl)-N-methanimidamide) is a formamidine compound. It is widely used to treat demodectic mange in dogs and as a prophylaxis against ticks in several species, including cattle, goats, and rabbits. Amitraz toxicosis is a rare clinical presentation. The mortality rate is less than 5% in dogs if appropriate treatment is instituted but is higher in young, old and debilitated animals and, reportedly, toy-breed dogs (e.g., Chihuahuas, Pomeranians). Intoxication is associated with cutaneous exposure to high concentrations of dip solution or ingestion of the solution or a collar containing amitraz. Amitraz is rapidly absorbed orally and transdermally. After ingestion, amitraz is rapidly hydrolyzed by gastric acid to its mono-N-methyl derivative, which is a more toxic compound. The peak plasma concentration occurs within 1.5-6 hours, and its elimination half-life can be as long as 24 hours. Elimination is mainly via the urinary tract, and small amounts are excreted in the bile. The elimination half-life of amitraz is dose dependent, and amitraz may take more than 72 hours to be completely eliminated. The LD50 of amitraz in dogs is 100 mg/kg. Toxic effects may be seen with doses of 10 mg/kg. Signs of toxicity may appear within 1 hour of ingestion and are mostly related to α2-adrenergic activity. Common clinical signs include cardiovascular, gastrointestinal (GI), and neurologic signs.

    Diagnostic Criteria

    Historical Information

    Gender Predisposition

    • None reported.

    Age Predisposition

    • Animals younger than 3 months and geriatric animals.

    Breed Predisposition

    • Toy breeds (e.g., Pomeranian, Chihuahua).
    • Cats are more sensitive than dogs and more likely to develop toxic effects.
    • Rabbits and small rodents are very sensitive to the toxic effects of amitraz.

    Owner Observations

    • Lethargy.
    • Vomiting.
    • Collapse.
    • Anorexia.
    • Dyspnea.
    • Polyuria/polydipsia.
    • Mild to severe depression (lasting 24-72 hours).
    • Ataxia.
    • Loss of consciousness.
    • Sedation.
    • Diarrhea.
    • Hypersalivation.
    • Death.

    Other Historical Considerations/Predispositions

    • Witnessed ingestion of acaricide-impregnated collars or pieces of collar.
    • Inappropriate direct application of amitraz-containing products.
    • Use of undiluted amitraz-containing products. After application of properly diluted and applied solution, toxic effects are less common and transient.
    • Toxic effects are more severe and recovery is slower in debilitated animals.

    Physical Examination Findings

    • Lethargy.
    • Ataxia.
    • Hypothermia.
    • Mydriasis.
    • Vomiting.
    • Dehydration.
    • Seizures.
    • Hypertension or hypotension
    • Sedation.
    • Bradycardia.
    • Tachypnea/dyspnea.
    • Diarrhea.
    • Hypersalivation.
    • Hypoperfusion.
    • GI stasis.

    Laboratory Findings

    • Hyperglycemia—common.
      — Secondary to effects on pancreatic bcells and consequent inhibition of insulin release.
      — Secondary to effects on acells of the islet of Langerhans and increased glucagon secretion.
      — May worsen clinical signs in diabetic animals.
    • Elevated liver enzyme activity—rare.
      — Secondary to metabolism in the liver.
    • Glycosuria.
    • Isosthenuria.
      — Secondary to glycosuria and decreased secretion of antidiuretic hormone and renin.

    Key To Costs

    Other Diagnostic Findings

    • Abdominal radiography. $
      — May help visualize a collar buckle in the stomach or small intestine.
    • Liquid chromatography. $$
      — Used to evaluate for the presence of amitraz in body fluids (i.e., gastric contents), plasma, and hair. This method has only been used to prove exposure and absorption as toxic levels have not been determined for tissue. (Only performed in specialized laboratories.)
    • Pathologic findings—mainly secondary to high-dose or prolonged exposure.
      — Increased liver weight.
      — Slight enlargement of hepatocytes.
      — Thinning of the zonae fasciculata and reticularis of the adrenal glands.
      — Slight hyperplasia of the zona glomerulosa of the adrenal glands.

    Summary of Diagnostic Criteria

    • Previous or suspected history of exposure to amitraz-containing products:
      — Application of acaricide collars.
      — Application of spot-on acaricide solution.
      — Bathing or dipping in amitraz-containing solution.
    • Compatible clinical signs.

    Diagnostic Differentials (Box 1)

    • α2-Adrenergic toxicity (e.g., medetomidine, xylazine).
      — α2-Adrenergic agonists are widely used in veterinary medicine for their sedative and analgesic effects. Toxicity may occur if these drugs are used inappropriately or if an overdose is erroneously administered. Clinical signs of toxicity include bradycardia, occasional atrioventricular block, decreased respiration, hypothermia, urination, and vomiting.
    • Organophosphate and carbamate compound toxicities.
      — These compounds interfere with the metabolism or breakdown of acetylcholine at cholinergic sites. Clinical signs can be grouped into three categories. Muscarinic signs are summarized using the acronym SLUD: salivation, lacrimation, urination, defecation. Nicotinic signs include generalized muscle tremors of head and body and generalized muscle fasciculation. Central nervous system (CNS) signs include anxiety and restlessness, seizure, and coma. Patients display classic miosis versus the more common mydriasis seen with amitraz toxicity.
    • Recreational drugs: opioids, marijuana.
      — Clinical signs associated with opioid intoxication in dogs include miosis, salivation, diarrhea, depression, bradycardia, and ataxia.
      — The clinical signs associated with marijuana intoxication depend on the effect of the compound on the cannabinoid receptor in the brain and include ataxia, incoordination, tremors, disorientation, bradycardia, hypothermia, hypersalivation, and mydriasis.
    • Prescription drugs: benzodiazepines, barbiturates, tricyclic antidepressants.
      — Benzodiazepines interact with benzodiazepine receptors that modulate GABA, an inhibitory neurotransmitter. Clinical signs are mainly tremors, ataxia, and CNS depression with no effects on the cardiovascular system.
      — Barbiturates activate inhibitory GABA-ergic receptors and inhibit excitatory glutamate receptors. They do not cause mydriasis. Clinical signs associated with intoxication include depression, ataxia, recumbency, coma, tachycardia, or bradycardia.
      — Tricyclic antidepressant drugs inhibit the fast sodium channels in the ventricular myocardium, causing a prolongation of the QRS intervals. The CNS toxicity is not fully elucidated. Clinical signs initially include hyperthermia, vomiting, hyperexcitability, tremors, and seizure and then progress to bradycardia, coma, hypotension, and cardiac arrhythmias.
    • Ethanol.
      — Ethanol affects the lipids and proteins of cell membranes, resulting in reduced sodium and potassium conduction in nerve membranes. Ethanol mainly causes signs of CNS depression. Other clinical signs include ataxia, lethargy, sedation, hypothermia, and metabolic acidosis.
    • Ethylene glycol.
      — Acute toxicity results in neurologic signs, including sedation and depression.
    • Pyrethrin and pyrethroid.
      — These compounds prolong the sodium conductance in nerve axons, resulting in repetitive nerve firing. Mild clinical signs are hypersalivation, twitching, paw flicking, mild depression, and vomiting. Moderate to severe toxicosis can cause protracted vomiting, diarrhea, marked depression, ataxia, muscle tremors, seizure, coma, and death.
    • Primary CNS disease.
      — History consistent with CNS trauma.
    • Diabetes mellitus.
      — Diabetes mellitus can occur secondary to a decrease or absence of insulin secretion by the pancreatic β cells or loss and/or inactivity of insulin receptors at a cellular level. This causes a failure of glucose uptake into the cells, leading to hyperglycemia, glycosuria, and cellular starvation. Clinical signs associated with diabetes mellitus are polyuria/polydipsia, polyphagia, and weight loss. Clinical findings are hyperglycemia and glycosuria.

    Box 1: Amitraz Toxicity

    Treatment Recommendations

    Initial Treatment

    • Mild, transient sedation after correct application of product.
      — This often does not require any specific treatment.
    • Mild signs after application of topical product.
      — Decontaminate skin by washing with mild detergent and copious warm water. Wear personal protective garments (gloves, apron).
    • Recent ingestion of a collar or pieces of a collar with minimal clinical signs.
      — Induction of emesis. As amitraz can delay gastric emptying, emesis can be induced for up to 12-24 hours.
      • 3% hydrogen peroxide at a maximum dose of 2 mL/kg PO can be used. Administer a maximum of 45 mL after feeding a moist meal.
      • Apomorphine 0.02-0.04 mg/kg IV, SC, IM. This may cause CNS and respiratory depression, so use only if there are no clinical signs.
      — Endoscopic retrieval of pieces in the stomach and small intestine if emesis is unsuccessful or there are small pieces in the small intestine. $$
    • Incomplete retrieval of collar in asymptomatic or mildly symptomatic patients.
      — Activated charcoal 2 g/kg PO. Oral activated charcoal-based toxin absorbers may help to bind any released amitraz. Charcoal may be readministered multiple times until the collar is retrieved or eliminated in the stools. This may prevent further absorption of amitraz from the collar.
      — Laxative. Administer a nonoily laxative (oil-based laxatives may increase the extraction of amitraz from the collar and facilitate greater absorption). An enema to evacuate the colon may be administered about 12-18 hours after ingestion, if diarrhea has not occurred or the laxative does not produce the desired results.
      — Bulky diet to decrease intestinal transit time. This can be used with charcoal and laxative therapies.
    • In patients with moderate to marked clinical signs after ingestion of collar or topical application.
      — Atipamezole: Specific α2-adrenergic antagonist. Starting at the lower end of the range, administer 0.05-0.2 mg/kg IM slowly. The IV administration of atipamezole is off label but could be considered in an emergency situation.
      • This will reverse bradycardia, sedation, hypertension, hypotension, and GI effects within 10-15 minutes.
      • Because atipamezole has a short half-life (1.5-2 hours), dosing may need to be repeated every 2-4 hours, particularly if the animal has ingested an amitraz-containing collar that has not been retrieved from the GI tract and there are persistent clinical signs.
      — Yohimbine: α2-adrenergic antagonist. Administer 0.1 mg/kg IV slowly or IM.
      • This will reverse bradycardia, sedation, hypertension, hypotension, and GI effects in minutes.
      • Because yohimbine has a short half-life (1.5-2 hours), dosing may need to be repeated every 4 hours, particularly if the animal has ingested an amitraz-containing collar that has not been retrieved from the GI tract and there are persistent clinical signs.
      • Yohimbine has been associated with tachycardia and tachypnea because of residual α1-adrenergic antagonism. It may also cause vomiting and shivering.

    Supportive Treatment

    • Fluid therapy based on maintenance fluid therapy and correction of any dehydration.
    • Maintenance of normal body temperature.

    Patient Monitoring

    Close observation for possible recurrence of clinical signs is advocated for at least 24-72 hours in moderately to severely affected patients. Important parameters to monitor are:

    • Heart rate.
    • Blood pressure.
    • Body temperature.
    • Urine production.
    • Serum glucose.

    Home Management

    If clinical signs are mild, the owner can be advised to bathe the animal with a mild hand soap or dishwashing detergent (owners should be advised to wear gloves to protect themselves from toxicity).

    Milestones/Recovery Time Frames

    • Mild and transient sedation after correctly applied treatment.
      — Recovery is expected after 24-36 hours.
    • Moderate to severe clinical signs after institution of treatment:
      — Reversal of bradycardia, hypothermia, depression, and sedation within minutes from antidote's administration, but it may take up to 24-72 hours for complete recovery.

    Treatment Contraindications

    • Use of atropine to reverse bradycardia.
      — Atropine does not reverse the α2-agonist effect of amitraz. It increases the heart rate and may potentiate hypertension.
      — The resultant increase in myocardial oxygen consumption may predispose patients to cardiac arrhythmias.
      — Atropine aggravates GI hypomotility.
    • Use of xylazine as an emetic.
      — This may increase the toxic effects of amitraz and worsen CNS depression.
    • Administration of insulin to correct hyperglycemia.
      — Inefficient in decreasing hyperglycemia. The administration of an α2-antagonist causes a rapid restoration of euglycemia.
    • Induction of emesis after ingestion of amitraz solution.
      — This may be ineffective because the peak of absorption through the GI tract is 1 hour, and patients rarely present this quickly. It may be contraindicated if the patient is sedated.
    • Gastrotomy to remove ingested collar.
      — Increases the risk of gastric dilatation secondary to gastrointestinal hypomotility.

    Prognosis

    The prognosis is usually good with rapid institution of treatment. Mortality from amitraz toxicosis is rare (<5%) in dogs. The prognosis is less favorable in cats.

    Favorable Criteria

    • Mild and transient sedation (24-72 hours).
    • Reverse of clinical signs (CNS depression, bradycardia, respiratory depression, and GI hypomotility) following rapid decontamination and institution of therapy.

    Unfavorable Criteria

    • Tachycardia.
    • Dyspnea.
    • Signs consistent with hypoperfusion.

    Grossman MR. Amitraz toxicosis associated with ingestion of an acaricide collar in a dog. JAVMA 1993;203(1):55-57.

    Gunaratnam P, Wilkinson GT, Seawright AA. A study on amitraz toxicity in cats. Aus Vet J 1983;60(9):278-279.

    Hugnet C, Buronfosse F, Pineau X, et al. Toxic and kinetics of amitraz in dogs. Am J Vet Res 1996;57(10):1506-1510.

    Oglesby PA, Joubert KE, Meiring T. Canine renal cortical necrosis and haemorrage following ingestion of an amitraz-formulated insecticide dip. Tydskr S Afr Vet Ver 2006;77(3):160-163.

    Queiroz MEC, Valadao CAA, Farias A, et al. Determination of amitraz in canine plasma by solid phase microextraction-gas chromatography with termionic specific detection. J Chrom B 2003;794:337-342.

    Richardson JA. Amitraz toxicosis. In: Peterson ME, Talcott PA, eds. Small Animal Toxicology. St. Louis: Saunders, Elsevier; 2006:559-562.

    Sakate M. The comparative efficacy of yohimbine and atipamezole to treat amitraz intoxication in dogs. Vet Hum Toxicol 2003;45(3):124-127.

    Click here to download this article as a PDF.

    Dr. Valtolina discloses that she has received financial support from Vetstream Ltd.

    CETEST This course is approved for 1.0 CE credits

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