I pulled this off a website for you...
Summary
Fipronil is a topical insecticide. It kills adult fleas and larvae, ticks, and chewing lice. It comes in two forms, a liquid that is applied to the skin along the back of dogs and cats, or a spray. If ingested, may see drooling. If irritation at the application site lasts for more than several hours, contact your veterinarian. Some animals may become hypersensitive (allergic) to fipronil.
http://www.peteducation.com/article....articleid=1419