Ivermectin Poisoning in Dogs
Ivermectin is a broad-spectrum antiparasitic medication. Its use for dogs includes treatment of lice, ear mites, heartworms, intestinal worms and mange. Although it successfully kills mange mites it hasn't been FDA (U.S. Food and Drug Administration) approved for this purpose. It's given orally or by injection daily or every other day. Toxicity can occur from one dose or several. According to the website "Petplace," "the most common causes of ivermectin toxicity are due to administration of excessive doses (10 to 20 times the recommended dose) and breed sensitivity."
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Fatal for Certain Breeds
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Sensitivity to ivermectin is most common in the herding breeds but it can be fatal to any breed or crossbreed. Collies, border collies, Australian shepherds, English shepherds, German shepherds, Shetland sheepdogs, Old English sheepdogs, McNabs, long-haired whippets and silken windhounds have the highest sensitivity rates, according to the Washington State University College of Veterinary Medicine website. A mutation in the multidrug resistance gene, MDR1, causes the drug sensitivity. Mutant MDR1 genes are unable to pump some drugs out of dogs' brains, causing neurologic problems and even death.
Testing Before Use
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Ivermectin sensitivity testing for the mutant MDR1 gene is available through Washington State University's College of Veterinary Medicine. Owners can order test kits by telephone or online. No training is needed to collect dogs' cheek swab DNA samples, which are returned to the university for analysis. Veterinarians submitting DNA do so via 2 cc of blood. Results take approximately two weeks. Although it says DNA testing is preferable, Mar Vista Animal Medical Center in Los Angeles says owners may try low dosages of ivermectin on their dogs prior to administering higher ones.
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Incompatible Drugs
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Ivermectin isn't compatible with the flea product spinosad (known as Comfortis), according to the website "Petplace." It shouldn't be used with valium or related tranquilizers. It also shouldn't be administered along with Amitraz or Mitiban mange dips or with Amitraz (Preventic) or other tick collars. According to Mar Vista Animal Medical Center, these medications are members of the monoamine oxidase inhibitor group. Their effects accumulate, creating sedation as well as adverse neurologic effects.
Poisoning Signs and Symptoms
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Signs of ivermectin poisoning occur acutely or subacutely. According to the website "Petplace," acute clinical signs often develop within four to 12 hours. Subacute signs often occur 48 to 96 hours after exposure. Symptoms of ivermectin poisoning include dilated pupils, depression, excessive drooling, vomiting, tremors, disorientation, weakness, inability to rise, blindness, nonresponsiveness, slow heart rate, lack of appetite, stupor, slow respiratory rate, seizure, coma or death.
Treatment
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"There are no specific reversal agents available to treat ivermectin toxicity," according to the website "Petplace." Treatment is largely supportive and symptomatic. The site recommends induction of vomiting, gastric lavage and activated charcoal to minimize absorption if accidental exposure is recent---within four to six hours. General care may include intravenous fluid and supplemental electrolyte therapy and intravenous or tube feeding. Recumbent (unable to rise) dogs receive appropriate bedding, frequent turning, physical therapy, eye lubricants, heat or fan support (depending on their temperatures) and urinary catheters. Respirators and seizure medications are sometimes needed. Prognosis depends on severity of clinical signs and the dog's individual response. Some take days or weeks to recover.
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References
- Photo Credit collie image by Ivonne Wierink from Fotolia.com
