I haven't personally because we don't use heartworm prevention that contains ivermectin.. we don't because we have the tortoise.
One of the yahoo groups I'm on, I don't recall which- about a year ago someone posted that their tortoise did die because it had eaten dog poop from a dog on ivermectin.
The person's vet confirmed it so I just won't take the chance.
Ivermectin exits a dog's body through the feces, it's too risky.
We use Revolution, I know there's another heartworm preventative for dogs that doesn't contain ivermectin but at the moment I can't recall what it is.
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PHRatz