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Ivermectin Toxicity in Dogs

This toxic reaction occurs especially in dogs that are genetically hypersensitive to ivermectin, an anti-parasite medication most commonly used for heartworm prevention, or to treat ear and hair mites, which can lead to mange. Ivermectin prevents or kills parasites by causing neurological damage to the parasite, resulting in paralysis and death for the parasite. But dogs genetically sensitive to the medication have an anomaly that allows the ivermectin to pass the dog's blood-brain barrier and into its central nervous system, which can be lethal for the animal.

While the sensitivity to this type of medication is not always guaranteed, the following breeds are most likely to be affected:

• Old English Sheepdog
• English Sheepdog
• Shetland Sheepdog (Sheltie)
• Australian Shepherd
• German Shepherd
• Long-haired Whippet
• Silken Windhound
• Skye Terrier
• Collie

It is also seen in mixed-breed dogs, older dogs that have experienced a blow to the head, puppies, and dogs that have overdosed on similar types of drugs. Treating dogs that are susceptible to ivermectin toxicity with parasitic medication should be only be done under a veterinarian's supervision and with great caution.

Symptoms

Symptoms for the dog may be acute or mild. Acute signs will become apparent within 4 to 12 hours of the drug's administration. In mild cases, symptoms will occur between 48 to 96 hours after your dog has been treated. Such symptoms include: 

• Lethargy
• Depression
• Drooling
• Vomiting
• Dilation of the pupil
• Loss of appetite (anorexia)
• Difficulty controlling voluntary movement
• Disorientation
• Tremors/Seizures
• Inability to stand
• Blindness
• Slow heartbeat
• Respiratory distress
• Coma