Question about Frontline Flea and Tick for cats???

I want to get that Frontline flea and tick stuff for my cat. I had gotten it two years ago when we had a terrible flea infestation of our home. My husband brought me home a kitten from a place on his way home from work that was advertising "Free to a good home". Little did he know that the kitten had fleas and regrattably infected the whole house and our other cat. Our other cat has since ped away, but we still have the original kitten. She is now flea free and will be 4 years old this Spring. I had gotten the Frontline for them when this whole thing happened, but our cat licked it off. Isn't that stuff poisonous? I haven't gotten it for her since because she is so flexible, that when you put it on her, she licks the darn stuff off and I don't want to make her sick. Is is OK to use this stuff, even though she can ingest it? I would think not, with all the warning lables on the back. Any input???