| The best thing to do is ask your vet for assistance. Ivermectin is not generally considered dangerous to give dogs that are heartworm-positive, although it is possible that they'll have a bad reaction if they have a lot of circulating microfilaria, according to what my vet says. So the best idea is still to test them before starting it. It will not cure them of heartworm infection, but it can keep them from getting even more heartworms (ivermectin kills the microfilaria). If the dog doesn't have a bad infestation, with the parasite's lifespan being a few years, it's possible after that time to end up with a heartworm-free dog. It can be better than doing nothing if conventional treatment isn't an option. Heartworm infestation does DAMAGE to the dog, and ivermectin (Ivomec) won't undo the damage. Please CONSULT A VET about this. Standard preventative dosage that I have been told by several vets over the years is one-tenth of a cc of Ivomec (which is a brand name) per ten pounds, given orally once a month. I do not have Collies or herding types, some individuals of those breeds can be sensitive to ivermectin, and I have never had problems with this dosage. Use a needle and syringe to withdraw the correct amount, remove the needle and squirt into the dog's mouth. My dogs won't take a treat with the stuff on it. Air and light are enemies of Ivomec. Keep the rubber stopper tightly in the bottle (which is why you need a needle and syringe) and store the bottle in a cool, dark place. It does not need refrigeration. The old medicine that was dangerous to give to heartworm-positive dogs was DEC, or diethylcarbamazine, also known as Filaribits. It was given daily. I don't know how or why the danger of giving that old medication to positive dogs got carried over to ivermectin, but it did. DEC hasn't been in common use, to my knowledge, for several decades. | 
