There have been some studies done on this, and many people have given dogs
liquid ivermectin as parasite control for their dogs. From what I have read on it, ivermectin in the
liquid form is more safe to give even if your dog develops heartworm than some of the products on the market.
HOWEVER (and that is a BIG however), you have to be
extremely cautious on dosage. Dogs need very, VERY little of the drug. They can very easily become disoriented, paralyzed, and even worse die from slight overdosing. I don't know what the off label dosage is for dogs.
The other
extremely important thing to know is what breed your dog is. There are several herding breeds (mostly the collie family, also Australian Shepherds, and I have heard German Shepherds as well) that have a very high sensitivity to the drug, which means the drug is pretty much lethal to them.
There is a test available through WSU that can determine whether your dog has the sensitivity or not.
http://www.vetmed.wsu.edu/depts-VCPL/index.aspx
Yes, I have had to treat a Cardigan corgi with the liquid ivermectin with no adverse effects, and I know of breeders out there who use it with no problem.
I would not suggest EVER treating a dog with paste ivermectin whatsoever.
~kathryn