Our vet gives Toto the Sentinel [sp?] for heartworm. When she was small she only got 1/2 tab once a month ... it was a big day for us when she got larger and could have a whole pill!
Also, during flea season, she gives Advantage. Again, when she was small she only got 1/2 the tube and later gratuated to a whole tube. Since she isn't around other dogs very often and seldom is on the ground, I don't have to use it very often. I don't think the summers here in Colorado will be as bad for fleas ... they are terrible in Alabama and Missy, the Border Collie, never misses an opportunity to put a "pawfull" on Toto!! You can rarely even
find one on Missy ... but if she gets within three feet of Toto, sure enough, Toto gets one!!