Do your rats have fleas..? Mine have never picked them up, even when the dogs had a really bad bout of them. I'm just curious... I didn't even know you could use Frontline on them, I'd always heard Revolution..
I do not suggest fiprinol sprayed on a rat for 2 reasons. First frontline is quite toxic to rats and should only be used in a well measured amount. That is not easily achieved with a spray (actually the reason I dislike sprays for all animals). 2nd small animals like rats suffer respiratory issues very easily. Sprays and powders are not suggested for applying any medication to rodents because of the potential lung damage from breathing them in. Always use a measured dose such as from a syringe for applying topical medications.