Frontline plus for dogs on my cat?

I used frontline plus for dogs (89-132 lbs) on my cats - whole dose, one cat has been whiny, the other kinda lethargic, both seem to eat less, it's been 3-days since application and they seem to be getting back to normal. Does this medication seep into their blood stream or get absorbed thru their skin. What else should I watch for, probably too late to try to wash off.