Interceptor doesn't work in the heart of the "South". Probably one of the worst where we live. We use Advantage Multi or have some owners who use ProHeart. Both have the same active ingredient. Studies are completed that demonstrate their effectiveness. Out of three local vets, no cases of heartworms on advantage multi while the others can't boast the same effectiveness.
Advantage Multi works well for fleas but is a weak tick protectant. We don't have a big problem in our area and out of 20 something dogs, have only had 1-2 ticks since the beginning of summer until now. However, when traveling up north I use a tick collar, Preventic. I have also been told that you can use such products as advantix if needed, use one on the first and one on the fifteenth. I always loved advantix too before we began using the Multi.
I have heard the same about Advantage Multi from a few highly respected(at least by me) trainers. I just wish they would come out with a solid form instead of the topical.
Then I ran into this concerning the ProHeart. When it was published/posted, I have no idea and take the info for what its worth....... http://www.spoiled-paws.com/ph6.htm
Here's another heartworm thread.....I've read about this problem 'til my eyeballs have popped out, and still don't have a good answer. I'm in the Midsouth---the Heartworm Capital of America---and have been dosing my 11 yr. old lab with 0.1 cc/10 lbs. body wt ivermectin since she was a pup. She had her last negative heartworm check in November. My daughters 2 labs (9 yrs. & 13 yrs.) are on the same dose with negative results. They're dosed religiously every month--no misses. Others have reported ivermectin resistance. Really wish I knew the answer. One reason I don't fully agree with the ivermectin resistance theory is that in our area, most dogs (and all coyotes) don't get heartworm protection of any kind. Seems to me that would create a 'refuge population' of susceptible worms which would delay or prevent resistance. Monsanto uses the 'refuge population' idea in their earworm resistant corn & cotton seed. I'd like for someone with more experience/education to comment on this...does my theory make sense?