Do some breeds, especially collies, have a problem with Heartworm disease prevention medication?
The normal dose is not a problem, but giving 10-20 times the normal Heartworm disease prevention medication dose is dangerous for dogs with collie genetics (Australian shepherds, shelties, collies, border collies). The normal dose that kills the developing Heartworm larvae is safe. Higher doses of these medications, such as those used in cattle and horses to kill intestinal parasites, can harm dogs with collie breeding. Latest research shows that all drugs of the macrolide family (ivermectin, milbemycin, moxidectin, doramectin, selamectin) can cause toxicosis in collie breeds.