Got this from a gal on one of the other dog boards I'm on.  Just passing it on.

There was a question posed on another board I frequent - here's the link to the thread

Trifexis has the same meds in it as Interceptor and Comfortis - it is not to be given to certain herding breeds (Interceptor) or to seizure dogs.

I've given the Trifexis to Archer & Zoe twice now and they have not had any ill effects from it. I use a mobile vet here in NC and I had emailed them because I was out of the Interceptor and had asked about my options and he is the one that suggested the Trifexis.  This was his response to me "Ok, the Interceptor and Sentinel are on back order for atleast 6 months. They do have a fairly new product called Trifexis that has been out for about 1 year. It is the hw and flea combined. It is cheaper than doing Interceptor/Frontline. It is a combination of Interceptor/Comfortis. Plus, they are offering a $10 rebate for every 6 m supply purchased".

 When Interceptor became unavailable I called our vet back in Florida and asked what they were using in it's place and they recommended Trifexis.  We happen to to take Cassie to our new vet in NC for her routine blood work for her Addisons and she wanted our dogs on Heartgard Plus and the topical Frontline Plus for the fleas and ticks. She doesn't like the oral flea medications and the Frontline Plus seems to be working just fine. We don't need the Preventic collars anymore. They all have had no ill effects from either and we've been using them for 6 months now. 

 @cooperdog   Hi.  I will be the last person to contradict what a vet says, however, I just want to let you know that all 4 of our dogs were on heartguard and one of them got heartworm......3 times!   The first time we treated it, the rest of the time we continued heartgaurd.   I have since heard from several people that there have been breakthru's with heartguard.  Do an internet search.  My breeder and my vet confirmed they have seen and heard this.  We switched from the heartguard and frontline (frontline did NOT work for ANY of our four!  I think it's the TEXAS fleas!)  It used to work great, but the last couple of years we haven't had the same amount of luck.  All 4 of mine are on Trifexis and with no side effects.....thank goodness.  I was TERRIFIED to try the Trifexis.  Had my Chocolate lab not tested positive KNOWING that I gave the medicine FAITHFULLY and ON TIME, and knowing that she wasn't throwing the pill up, etc., I new we couldn't stay on Heartguard.  My next choice was Advantage plus.   Our vet quit carrying both Sentinel and Advantage plus......pretty much leaving us with one option that sounded reasonable.   I'm not trying to persuade or influence your decision, or to go against your vet at all... Just encouraging research.  If Heartguard works for you, that's wonderful!   

I had not heard that about heartgard, but I too am using Trifexus on all four of my dogs, two GSPs, a lab and a border collie.  I have had no issues now going on 4 months.

Roz.

 Yes, therozypozy.   We are also using Trifexus on our Aussie/Brittany mix.  Experts warn against using it on cattledogs of the shepherd/collie breed, however, our mix has not been affected in any way.  If you google the heartguard breakthru, you should be able to find something.  I did, just don't remember where!

there is ivomectin resistance...loved interceptor..also..fipronil in frontline..has been around for  about 20yrs..we are seeing fleas on pets, prob also building up resistance..hate to say..frontline isnt working like it had in the past...