We have not had good luck with Frontline, and it's expensive for us - 140 lb dog. 75 lb dog. Miss Pootie refuses to give her accurate weight like any Southern lady in public forced upon the scales of injustice at the veterinary office. (you should see the look she glares at the vet attendent) it's nearly comical.
So we started trying Capstar (or it maybe called Capstone) capsules, which will kill fleas in about 15 minutes, and then you have to give another dose in about 7 days. Pills are around $6.00 each. In the interim? We mix up Diatamtious Earth (the edible kind) An entire jug of this stuff sold at our local pet rescue is only $8.95 and you mix it either in their food or like we do with milk, and they love it! For the first week? They get it every day. For every subsequent week? Once a week. You can even use it as doggie toothpaste, and for dusting the furniture, or carpets - you can eat it - I did, it's just like chalk.
NOT any diatamateous earth, this is the EDIBLE kind. But it works GREAT and for Casper the sensitive albino kid? NO BLISTERS this year - NONE, NADA, ZIP.
Fleas have no circulatory system so when they bite the dog, and injest this stuff that is in a dogs blood stream? They literally BLOW UP. (I think I have that right) I'll double check but they do blow up. And we haven't had a flea for almost a year. If they HAVE fleas - ask for the Capstar/capstone - and in 15 minutes? The fleas are DEAD/bang gone. Then do the powder in the food. We get cheap cans of milk....it's "treat" time. For Ace he'd probably get 1 TBS a day for 1 week and then 1 TBS a week - for the rest of his life.
All natural - and safe, and I get a discount for bringing the jug back, and it supports the animal mission.