Pyrethrin-based flea preventative not working
For the first time we are seeing fleas on our dog. We've been using a pyrethrin-based product. It has kept her flea-free for a year but isn't working anymore. We last treated her a week ago. Since it isn't working is it ok to use a different medication on her with fipronil, or do we have to wait another 3 weeks? I heard on the radio that the fleas may become resistant to one type of chemical and you might have to switch to another, but don't want to do something that will hurt the dog.