I just found this about advantage multi. So maybe it is a good/safer product? Also compares some of the others.
“Advantage Multi
Moxidectin is a remarkable substance that is both safe and effective as a heartworm prevention. Advantage Multi is a topical solution for application to the pet’s skin once a month.
It is the only heartworm prevention that may be given to heartworm positive dogs.
It is the only heartworm prevention that is effective against all strains of heartworms identified.
It is the only heartworm preventative that kills early L5 or young adult heartworms.
Advantage Multi is a combined product of Moxidectin which prevents heartworms and controls intestinal worms (hookworms, roundworms and whipworms) combined with imidacloprid which kills adult fleas. I recommend Advantage Multi as the best Heartworm Prevention Available today. It has a broader range of effectiveness against the life stages of heartworms and is also effective against more species of intestinal parasites as well. It is safer than other products in the same category and can be given to puppies at 7 weeks of age and to heartworm positive animals. There is a new concern that heartworms are developing resistance to heartworm preventions. See this article that compares Advantage Multi to all the other common heartworm preventions.”
Heartworm Prevention Dogs
Also found info on heartworms, treatments, etc. here;
http://www.heartwormsociety.org/pdf/2014-AHS-Canine-Guidelines.pdf
