danna is right. Hartz is killing dogs and the company doesn't seem to do anything about it. Lily's Frontline Plus is a topical - I wasn't aware they made an oral med. Advantage has ivermection in it and collie type dogs can't have it without a blood test to see if they carry a certain gene. So much to think about, but once you see a flea, you need the big guns. Google Cedarcide - it kills fleas in the house and yard, but I never sprayed the dogs because I wasn't positive it was as non toxic as the company says it is.