#To clarify: proheart binds the moxidectin into “slow-dissolving microspheres”

[quillpenkeyboard]

Heartworm prevention is only effective on heartworm larvae younger than a certain age, which is why the standard kind has to be given monthly.

We can only test for fully adult heartworms, which means about 6 months after the mosquito transmits them - so there's a blind spot when you start prevention where you *could* be infected and too late to prevent but too early to detect. This is why most places still retest regularly even when you're on prevention.

How long does ivermectin (heartworm prevention) stay in a dogs system?

vet-and-wild here.

I'll give a little caveat that I'm most familiar with Heartgard, because that's what my clinic uses. Heartworm medication basically works by back-treating infections before the larvae can grow and cause disease. This is different than how most flea/tick meds work, because those are providing forward prevention. Meaning, when you give heartworm medication you're basically treating for the previous 30 days (or whatever the product is labeled for). Conversely, flea/tick meds are treating for the following 30 (or whatever) days. So heartworm meds aren't really in the system for very long.

Keep in mind that this is different from something like ProHeart, which has a different active ingredient (moxidectin). ProHeart shots work more like standard flea/tick meds that provide protection forward from the point of administration.