Ivermectin is a medication in many heartworm treatments and often included in flea treatments too. For most dogs, this poses no problem. However, Ivermectin can potentially pose a danger to your dog if they are Ivermectin sensitive.
Certain dogs are more susceptible to neurotoxicosis when administered doses of Ivermectin. And, neurotoxicosis is an acute neurological attack that is frequently fatal. Not what you want from your heartworm medication!
What is Ivermectin Sensitivity?
The brain normally protects itself from the accumulation of medications in the bloodstream with a barrier. In some dogs, this barrier malfunctions due to a genetic defect of the MDR1 gene.
The MDR1 Gene
The MDR1 gene protects your dog from a fatal accumulation of medication in the brain, particularly Ivermectin. Dogs who have the MDR1 gene have a healthy brain barrier.
Unfortunately, many dogs have a mutated MDR1 gene, causing neurological issues when exposed to Ivermectin. However, even with the presence of the gene mutation, Ivermectin is not always dangerous.
Heterozygous vs. Homozygous
The MDR1 gene mutation is a recessive gene. The recessive gene becomes expressed only when it is homozygous. Genotypes are pairs of genes. They can be homozygous (two of the same) or heterozygous (one of each). When the MDR1 mutation is homozygous it causes Ivermectin sensitivity.
The parent can pass the gene to offspring when it is heterozygous. But normally doesn't cause sensitivity. Heterozygous dogs can sometimes be sensitive to Ivermectin to a lesser extent. Homozygous dogs will pass the gene on to offspring. As a result, they will be sensitive to Ivermectin themselves.
When Your Dog is at Risk
Even a dog with the MDR1 gene mutation will not necessarily have a reaction to any Ivermectin exposure. A sensitive dog can take this medication. But only at the monthly preventative dose. They can be in danger when you give a dog higher dosages of Ivermectin.
This can be worse when the dog has mutated MDR1 genes. Dangerous dosages would include those for the treatment of heartworm. High doses of Ivermectin are used occasionally to treat Mange infestations. Either of these treatments would be dangerous to an Ivermectin sensitive dog.
Which Breeds Are Prone to Ivermectin Sensitivity?
Collies have the highest possibility of a mutated MDR1 gene. Australian Shepherds and mixed herding breeds have the next highest possibility of mutation. Shelties, Border Collies, Old English Sheepdogs, and German shepherds also have a small likelihood of an MDR1 mutation.
Collies have as much as a 75% chance of a mutated MDR1 gene. Australian Shepherds have a 50% chance of the gene occurring. Mixed herding breeds have a 35% chance of gene mutation. Other breeds range between 5%-10% likelihood of a mutated gene occurring.
You will not expose your dog to high doses of Ivermectin in most cases. However, if you do expose your dog to high doses, they could be in extreme danger. You should also be aware that herding breeds can also be exposed to Ivermectin. And that can be through the feces of recently wormed livestock.
With this in mind, it is important for you to be mindful of what your dog is facing every day. As a pet owner, you need to know if your dog is at risk.
The safest way is to test your dog for the MDR1 gene mutation. This can be done by getting The Animal Health Trust's test done on your dog. By understanding that your dog is at risk you can take the proper precautions for their safety.
Summary
As pet owners, our foremost duty is keeping our dogs healthy and safe. With that in mind, it is important to know what ailments your dog breed is prone to. Different dog breeds have different sensitivities and disease. As a dog owner, it is important to acquaint yourself with the dangers Ivermectin can present to them.