However there maybe other ingredients that wouldn't be good for dogs or the division of the medication might not be straight forward depending on it's form.
Most drugs are not just simply the drug.. There are all kinds of inactive things mixed in for various reasons.
If you have a prescription and you go to CVS to fill your dog's medication you are getting the exact same thing
If you go to Rural King and by a Tube of Horse Paste, you are not...
In the case of ivermectin tablets, usually available in 3mg, 6mg and 12mg versions both for dogs and for humans, there is unlikely to be any difference, and where I live the price is pretty much the same too.
Overdosing is not a concern of mine. Efficacy is my primary concern.
What dosage was used to cure or reduce symptoms of COVID based in well controlled clinical trials?
No you don't. Your vet does.