What if my dog ate two Trifexis? Here’s What to Expect

Is an online vet visit just as good as a trip to your veterinarian? No! But, many times, asking an online veterinarian a question can help save you money. While Dr. Marie cant officially diagnose your pet or prescribe medications, she can often advise you on whether a vet visit is necessary. You can also ask Dr. Marie for a second opinion on your pets condition.

Dr. MarieDr. Marie is a veterinarian who practices in a busy animal hospital in Ottawa, Ontario. She created Ask A Vet Question as a resource for good, accurate veterinary advice online. Dr. Marie treats dogs, cats, hamsters, guinea pigs, and rats. She has been a vet since 1999.

Signs of a Heartworm Medication Overdose

Heartworm preventatives belong to a family of drugs called the avermectins. As Parasitipedia explains, in overdose situations, these drugs interfere with nerve transmission and cause the central nervous system to respond abnormally to stimulation. Typical symptoms include:

  • Ataxia: The dog displays uncoordinated movements, staggers, or appears drunk
  • Goose-stepping: Taking exaggerated steps where the paws are lifted too high
  • Disorientation: The dog appears confused
  • Hyperaesthesia: The dog jumps in an exaggerated manner in response to touch or quiet noises
  • Mydriasis: The dogs pupils are dilated
  • Drooling: The dog salivates excessively
  • Trembling: Shivering and shaking in an out-of-control manner
  • Depression: The dog is unusually quiet and difficult to rouse
  • Coma: Loss of consciousness
  • If your dog displays any of the above symptoms, especially after an overdose of heartworm medication, contact the vet immediately. While there is no antidote to toxicity, the vet may be able to give medications to minimize further absorption of the active ingredient and to reduce the effect of the toxicity.

    Several breeds have a hereditary sensitivity to ivermectin, but the following breeds are the most commonly affected:

    A mutation in the MDR1 gene is responsible for this genetic susceptibility. This mutated gene may also make the dog more sensitive to a variety of other drugs. Individual dogs of the above-mentioned breeds do not all possess the mutant gene. Testing is the only technique to determine whether a dog possesses the mutant MDR1 gene. To perform the test, cells from inside the dogs cheek are scraped or a blood sample is taken and sent to a lab for genetic analysis. If youre interested in getting your dog tested, talk to your veterinarian.

    Your vet is always the best source of information pertaining to your specific circumstances and the information below is provided for general interest only. Follow all veterinary advice and do not attempt to treat your dog without guidance from your veterinarian if you suspect an overdose has occurred.

    The greatest risk with expired medication is that it has lost some of its effectiveness. Therefore, if the dog eats a recommended dose of an expired med, contact your vet to inquire when you should give the next dose of in-date medication. The answer will vary depending on the conditions in which the medication was stored and how out of date it was.

    Because the medication will have some residual action if the dog has an overdose, contact the vet as you would if an overdose of an in-date medication had been given, and proceed accordingly. Using out-of-date medication means there is a risk the dog was not protected and may have picked up heartworm in the interim. You must discuss this with your vet because treating with a preventative if the dog has adult heartworms could make the dog very sick.

    Collies, in particular, are a special case. Some Collies have a genetic mutation which makes their brain more vulnerable to the effects of ivermectin medications. Always contact your vet immediately if your collie has an overdose. Plumbs Veterinary Drug Formulary suggests signs of toxicity are most likely to occur with doses in excess of 1 milligram per kilogram of body weight (equivalent to 1,000 micrograms per kg of body weight). Thus, a 10-kg (roughly 22 pound) dog may show toxicity when exposed to 10 mg (or 10,000 micrograms) of ivermectin.

    A single dose of Heartgard Plus for a dog weighing less than 25 kg contains 68 micrograms. Thus, the same 10-kg dog would need to eat around 147 tablets for an overdose to occur. However, some dogs are more sensitive to the active ingredients than others. Never be complacent and always seek veterinary advice if the dog may have had an overdose.

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    Does Trifexis Flea Medication Work?

    You do the responsible thing and regularly treat your dog against heartworms, but then your pooch accidentally gets a double dose of heartworm medication and your panic begins. Its helpful to know when you should contact the veterinarian and the signs of heartworm medication toxicity to watch for.