I was looking up some holistic vets in my area and I was surprised to see they charge the same as conventional vets. I talked to the vet tech for 20 minutes and she told me they DO NOT reccommend Sentinel because it is too harsh on the liver and kidneys to process. They reccommend Hearguard and Advantage topical. She said the topicals are safer and the liver does not have to process. I don't know about that.....