I bought the "Frontline Plus" for my baby a few months ago. I have applied two applications since I bought it. I purchased a box that has 3 applications in it. I read to use it once a month, 3 apps. a package cost me around $45 bucks! However, the vet said I could possible use it once every other month, but I don't trust that in the summer months. We have plenty of dogs, mosquitos, etc. you name it around us. So I've been using it every month. So far, THANK GOD, my baby is just fine.
Anyway, I wanted to comment on the directions per box. The have the weight of the dogs as to what box to use. The one I use says it's for dogs up to 22lbs! My dog is 8.5lbs and this is the box my vet recommended. And he said to use the ENTIRE package at a time. So this is how I use it. Each box has different weight requirements. All dogs under and up to 22lbs is the box I use, tho. I was concerned about my dog using it and he is nowhere near 22lbs. However the vet said it was designed to be used this way..If you find out something different, please share your info. =)