Quote “So if you’re worried give half the chew one day then the rest the next day so they aren’t getting such a huge dose immediately” .
The full dose needs to be given at the same time for the drug to be effective. The combined ingredients work together and the drug is out of the dog’s system within 24 hours. They kill the mosquito larvae that may have developed the month prior, not the month ahead.
http://news.petmeds.com/news/pet-meds/why-you-should-not-split-heartworm-medication-between-dogs/
“When splitting oral heartworm medication (especially soft chews), it is possible that you will not divide it evenly thereby resulting in one dog getting a smaller or larger dose. Additionally, oral heartworm medications have the active ingredients blended throughout and while theoretically the active ingredients are evenly distributed, there is no guarantee that there will be an equal concentration of the medication in each part. So, even if you’re able to split the chew exactly, one half could still have a higher or lower concentration of the active ingredients”
