Once Frontline Plus active ingredient fripnol made it past the patent point and a lot of other flea meds with the same active ingredient in it, Frontline Plus started to be ineffective on my dogs. I went to Banfield and purchased First Shield Trio, which has the exact same active ingredients as Advantix II (Advantix has a higher concentrate though), my dogs were immediate relieved of fleas again.
Just like a human, every animal has its of specific allergies. My large dog gets skin infections from certain shampoos, or fresh grass. Therefore, it is possible that your dog may not of been allergic to the active ingredients rather the inactive ingredients. I have scene quiet a few dog burns online due to topical medication.
However, the pill form of flea meds cause my parents Jack Russell to become ill, and hospitalized to flush his system. It was a completely different vet.
So don't judge a vet based on a product as we all have allergies and your poor baby may have just had an allergic reaction. Sorry to hear of your experience.
Product or Service Mentioned: Schuyler First Shield Trio Flea Control.
Reason of review: Good quality.