@JaxTabby,what you can do if the safe topicals are not working on the fleas is (1) treat the environment (assuming they are inside) with DE (diotomaceous earth, the edible kind you can get at flea stores) and you can use it as a flea powder on the cats as well; and (2) daily flea combing and knocking live fleas out of the flea comb into slightly soapy water in a bowl (we call that making flea soup) may not have them 100% clear but will help them a lot. Remember, unless the flea infestation is massive and the cats are kittens, fleas are unpleasant but not life threatening. Some of these chemicals ARE life threatening to SOME animals. Just like humans, some people are allergic to things that others are not, and allergies (like to peanuts) can be bad enough to kill you. Cheristin has enough bad history that it is not something I would ever try on any cat.
@ADoug, your vet is very narrow minded. After reading this thread, surely you can see that some cats have serious problems with this, and your vet should have considered this one cat may be allergic. I think you should get her to another vet, preferably at an accredited animal hospital (AAHA, you can search them here: https://www.aaha.org/pet_owner/about_aaha/hospital_search/default.aspx
It sounds like she needs immediate help and should have blood tests run to see if her kidneys and liver are functioning properly. Hopefully it isn't too late to save her.
@ADoug, your vet is very narrow minded. After reading this thread, surely you can see that some cats have serious problems with this, and your vet should have considered this one cat may be allergic. I think you should get her to another vet, preferably at an accredited animal hospital (AAHA, you can search them here: https://www.aaha.org/pet_owner/about_aaha/hospital_search/default.aspx
It sounds like she needs immediate help and should have blood tests run to see if her kidneys and liver are functioning properly. Hopefully it isn't too late to save her.