Giving a Cat Different Flea Medication?

I almost killed my cat with Hartz over the counter flea medicine. Took her to the vet and she said to use Ivory or Dawn, wash several times. I did so and she was feeling better within a day. Now, despite the cost (our animals are worth it) I buy the more expensive flea stuff. I would give the kitty a good washing (won't that be fun!) and give it a day or two, then add the newer stuff.

P.S. Try Foster's and Smith, they usually have good sales and even if they don't they have the best prices on the internet for flea meds. The last time I bought some from our local low-cost spay neuter clinic, with shipping from Fosters, it was the same AND I got one free vial. I use the kind that is the same no matter the weight, as I have one 8# and one 11# cat!

Warning, if your area is cold, DON'T wash the whole cat, heeding the vet's advice, because cats get colds
VERY easily and often die from it. I'd suspect that your carpets need a BETTER vacuum, then toss the
bag. I have a Hoover WindTunnel with a dirt sensor light, picking up LOTS more dust particles/smaller things than most vacuums. Call around to repair shops since one part on them usually breaks, but

it has almost the best suction you can buy! It should pick up any fleas/eggs, and vacuum all furniture, inside/out, throw pillows, sofa cushion covers removed/turned, all baseboard edges, any pet areas
..if indoor cat. My cats only got fleas if they were outdoor cats, so I got wise and kept them indoors from birth, so they don't miss what they never had.
Once you get rid of the fleas/eggs in the carpet, please treat the perimeter of your home, if possible.
It's likely they are coming in to warmth because of the cold and to get "your cat's fresh blood", so to speak? Have you brought in any new upholstered
furniture in the last 6 months? I understand fleas
reproduce OFTEN and FAST, so it could even be something you might have brought in more recently.
Have any friends brought in pets, or have you taken your pet anywhere they could have gotten fleas,
such as a park or in an old vehicle with open windows? Second hand rugs AND public laundries
often have flea eggs. Investigate well, and try to solve the origin of the fleas as well as using better
powder mostly on back, top of tail, top of head
where the cat can't reach so well, then use it outside
or in garage, and sparsley to avoid accidents. God bless your efforts and give you endurance to not give up until total success!