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Accidentally gave my dog two Heartgard doses in 4 days. Is it safe?

Updated on September 23rd, 2025

I've given my dog two doses of heart worm medicine only 4days apart. He's a German Shepherd, 3 years old, 71 pounds, in great health. Heartgard Plus, dose 272 msg Ivermectin and 227 mg Pyrantel.

3 Answers

Most Helpful Answer

Dr. Melanie, BVSc MS

Answered By Dr. Melanie, BVSc MS

Veterinarian

Published on January 4th, 2017

The good news is that Hartgard is a relatively safe drug, and it is difficult to overdose dogs with the medication. Typically, toxicity is worried about when the dog ingests 10-20 times the recommended dose. Your dog should be just fine :-)
Vote Icon2Pet Parents found this answer helpful

Related Answers from Veterinarians

  • Answered By Sara Farmer, DVM

    Veterinarian

    Published on April 9th, 2018

    In general, most heartworm preventatives are very safe and it would not be harmful to give a double dose. Ivermectin and milbemycin (the active ingredients in Heartgard and Interceptor) are sometimes given daily for certain conditions. It would however help to know exactly what medication may have been given to know exactly what the risk might be. If Kobe has any other medical conditions there might be some concern and you should contact your veterinarian or the Pet Poison helpline at http://www.petpoisonhelpline.com/contact/

    Vote Icon

    1Pet Parents found this answer helpful

  • Answered By Jennifer Summerfield, DVM CPDT-KA

    Veterinarian, Certified Dog Trainer

    Published on June 18th, 2019

    Hi there. Heartgard is extremely safe, and would not harm a dog even if given multiple doses on the same day. So a second dose two days later should not cause any problems. You can just resume her normal dosing schedule next month.

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    1Pet Parents found this answer helpful

Smart Picks for Smart Questions

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My dog accidentally got an extra dose of heartworm medicine?
If it was Heartgard, there is no cause for concern. It is an extremely safe product and very difficult to overdose. If it was a different preparation of ivermectin, a double dose may not be cause for concern unless your dog is sensitive to it or carries the MDR1 gene. Typically, a non sensitive dog requires dosing around 2000mcg/kg before clinical signs become apparent. See your vet for an exam as soon as you can if you are concerned. Bring the container of ivermectin with you. Treatment for ivermectin toxicity is supportive in nature. Monitor for vomiting, excess salivation, ataxia (wobbly gait), dilated pupils or tremors.
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Can I give two smaller Heartgard Plus doses to my large dog?
Yes, you can give Fern two doses of the Heartgard so that she will get the correct amount of medication. Heartgard is a pretty safe drug, and you would need 10 to 20 times the recommended dose to see toxicity; however, in this case, because two of the chews from the green pack equals the same amount of medication in one chew from the brown pack, it's safe to give to her. I hope this helps!
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My dog accidentally got a double Heartgard dose. What to watch for?
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My dog ate too many Heartgard Plus pills. Should I call the vet?
Heartgard Plus has a very high margin of safety, so I would not expect this to cause any serious problems. I would recommend monitoring her for the next day or two to make sure that she's acting normal, but otherwise you shouldn't need to do anything different :) You can go ahead and give her next dose on April 15th as scheduled.
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My dog missed heartworm medicine. Can I give another dose safely?
Most of the monthly oral preventatives have a wide safety margin. Heartgrad is very safe, so if that is the preventative you use, then a second dose will not be harmful. If you use a different medication, check with your veterinarian before giving another dose.
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