Hello, my name is***** and I have over 20 years of experience as a veterinarian. I understand that you are concerned about dosing your pup with her heartworm prevention medication 2 days earlier than scheduled.
You don't say which prevention you are using to prevent heartworm. Common ones contain ivermectin, selamectin or milbemycin as the active ingredient to kill heartworms.
If the prevention that you use contains these medications it is perfectly safe to give it early. There are a couple reasons why it is fine to give it early.
These monthly heartworm prevention pills or topicals contain medication that kill heartworms at a certain stage of their life cycle. The medication does not persist in the body, it kills the parasite if present and the medication is cleared from the body in about 48 hours. You won't be overdosing your dog because last month's dose is long cleared from her body.
Most monthly heartworm preventions only need to be given at a low dose to kill that particular stage of heartworm. These medications can often be given at doses several times higher than that prescribed to kill heartworms to treat other parasites like sarcoptic or demodectic mange
. That means even if you accidentally double dosed (gave two doses in one day) she would most likely suffer no ill effects.
In short if you need to give her medication a couple days early that is perfectly fine.
Please let me know if you have any further questions.