Parasite Drug (Ivermectin) Poisoning in Dogs

Ivermectin Toxicity refers to overdose (10 to 20 times the recommended dose) of the drug ivermectin or due to hypersensitivity of the dogs to this drug. 

Ivermectin is a commonly used parasite drug that causes neurologic damage to the parasite, resulting in paralysis and death. Ivermectin has been used to prevent parasite infections, as with heartworm prevention, and to treat infections, as with ear mites which can cause Mange.

In certain dogs that are genetically hypersensitive to the medication, ivermectin can pass directly to the brain and be toxic or even lethal.

Hypersensitivity to this drug can be seen in several breeds but 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


This genetic sensitivity is due to a mutation in what is called the MDR1 gene. This mutant gene may make the dog more sensitive to several other medications as well. Not all individual dogs in the breeds listed above carry the mutant gene. 

Other dogs include mixed breed dogs, dogs that have suffered head trauma and dogs that have overdosed on similar types of drugs. 

Signs and symptoms for this condition may appear within 2 to 12 hours of drug administration in acute cases while in mild cases, symptoms will occur between 48 to 96 hours after the dog has been treated. Such symptoms include





Dilation of the pupil

Loss of appetite (anorexia)

Difficulty controlling voluntary movement



Inability to stand


Slow heartbeat

Respiratory distress


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