Ivermectin is a widely used antiparasitic medication for dogs. This medication is part of a class of drugs known as macrocyclic lactones. It works by impairing the nervous system of many parasites, leading to their paralysis and eventual death. Ivermectin is effective against a broad range of parasites, notably those causing severe conditions in dogs such as heartworms. It also combats mites responsible for diseases like demodicosis in canines. Among various brand names, Heartgard® stands out as one of the most well-known heartworm preventatives on the market. It uses ivermectin as the main active ingredient.
Here’s what you should know about ivermectin’s uses, dosage, and side effects for dogs.
Ivermectin is primarily used in dogs for the prevention and treatment of heartworm disease. The parasitic worm Dirofilaria immitis, living in the heart and pulmonary arteries of dogs, causes this disease. The drug works by killing the heartworm larvae, preventing them from maturing into adults, which can cause disease.
Beyond heartworm prevention, ivermectin is also utilized in treating various other parasitic infections, including mites that cause mange — both Sarcoptes and Demodex —and certain internal parasites like roundworms. In some cases, veterinarians may prescribe ivermectin off-label to manage external parasites such as fleas and ticks, although it’s not the primary treatment choice for these infestations.
You can use ivermectin alongside other deworming medications for a comprehensive treatment. It comes in various forms, such as tablets, chewable tablets, topical liquids for ear mite treatment, and an injectable form that your veterinarian will administer.
Ensure you store products containing ivermectin at room temperature in a cool, dry area. Furthermore, avoid exposing them to heat and direct sunlight, as such conditions can diminish the drug’s effectiveness.
The following is a guideline for the typical use of the drug in dogs and must not replace your veterinarian’s advice for your individual pet.
The dosage of ivermectin prescribed for your dog can vary significantly based on your pet’s condition, weight, and sensitivity to the drug. It is critical to follow the veterinarian’s prescription precisely, as incorrect dosages can lead to ineffective treatment or severe toxicity.
For heartworm prevention, the typical dose is relatively low, at 0.0015 – 0.003 mg per pound of body weight, administered orally once a month. For the treatment of mange, doses can be higher and might require administration under strict veterinary supervision.
You can give ivermectin to your dog with or without food. However, if your pet shows signs of sickness or vomits after taking ivermectin on an empty stomach, try accompanying it with food or a small treat to improve tolerance. Should vomiting persist, consult your veterinarian for further advice. If you are using the topical form of ivermectin, your vet will offer detailed guidance on how to correctly apply the medication to your dog’s ears for optimal results.
The duration for which your dog should stay on ivermectin largely depends on the condition under treatment and your veterinarian’s recommendations. When used for heartworm prevention, you typically give ivermectin monthly throughout the year, or at least during the mosquito season if you live in an area with a seasonal risk. The American Heartworm Society recommends year-round prevention. For treating conditions like mange, the treatment period might range from several weeks to months.
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While ivermectin is generally safe for most dogs when used according to a vet’s prescription, it’s important to be aware of potential side effects. These may include:
Vomiting
Diarrhea
Lethargy
Loss of appetite
Dilated pupils
Unsteadiness or ataxia
Seizures (in severe cases)
These side effects can range from mild to severe and usually occur if the drug is overdosed. Moreover, certain breeds, like Collies, Shetland Sheepdogs, Australian Shepherds, and other herding breeds, are more prone to ivermectin toxicity. This susceptibility is due to a genetic mutation — MDR1 gene mutation — that affects the dog’s ability to process the drug, leading to an increased risk of adverse effects.
Certain medications can increase the effects of ivermectin on your pet’s brain. These include ketoconazole, itraconazole, cyclosporine, erythromycin, amlodipine besylate, and nifedipine. When administering high doses of ivermectin for mite infestations, avoid giving spinosad or Comfortis — a typical flea preventative — as it may interact negatively. However, spinosad remains safe for use with low doses of ivermectin found in heartworm prevention treatments. Always inform your veterinarian about any medications — including vitamins, supplements, or herbal remedies — your dog may be receiving.
Veterinarians do not recommend using ivermectin for dogs younger than six weeks of age or those without a recent negative heartworm test. If you notice any unusual symptoms in your dog after administering ivermectin, it’s critical to contact your veterinarian immediately. Your vet may recommend a specific treatment plan, including supportive care or administering a different medication if an adverse reaction occurs.
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