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Updated on September 23rd, 2025
Pet's info: Dog | Border Collie | Female | spayed | 4 years and 3 months old | 45 lbs
How do heart worm preventions work? I split the dose on the same day to prevent stomach upset. What if I divided 1/2 dose one week and remaining in 2 wks? Would it still be effective? Or do you have to give all of the dose at once. Dose it kill larvae once a month or is it lingering in the system the whole month?
2 Answers

Answered By Susan England-Foster
Veterinarian
Published on August 1st, 2017
Answered By Robin Diers, DVM
Veterinarian
Hello. You need to give the whole dose at the same time for heartworm prevention to be most effective. The preventative kills the larvae at one time, it does NOT linger in the bloodstream. If the medicine is making Jolie sick, talk to your vet about a preventative that will be easier on her stomach.
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