I've used Advantage on my greyhounds (also whippets and cats) for many many years with no problems

Last year I tried Advantix and one greyhound and one whippet had what I have to believe was a reaction - diarrhea and throwups

and general malaise for 24-48 hours after application. I'm back to using Advantage with no problems. Since then, I've been told that the chemical in Advantix that is supposd to help keep mosquitoes away is only effective for a few days at most - so not worth the extra cost or the risk of reaction for me!