I have 4 dogs from 3-8 lbs. and we have always used the Revolution. It is for fleas and heartworms in one dose. It goes on the back of their necks once a month. My 2 little ones (3 lbs. and 3.5 lbs.) use the under 5 lb dose. My 6 lb and 8 lb yorkies use the 5-10 lb dose. I like it because it is formulated by thei weight that is close to what they are. The ones that are for 1-25 are wayyyyyyyyyy too strong IMO and can cause problems. I have never had any problems or reactions from my girls using this. We have never had a flea.
