We have ours on trifaxis for fleas, worms, heart worms it was working well until this dry weather now we have fleas but it must be from the cats. Dh is going to spray outside the house soon, he treated the cats. The best way I get the fleas off the dogs is to give them a bath every few days. We didn't have any problems last year, it must be this weather.
trifexis is comfortis plus heatworm stuff, if you already have your dogs on heartworm stuff, like heartguard or proheart, just get the comfortis.