Dear Priscilla, It really depends how many fleas are there in your area. The thing withCapstar is that it only kills the fleas found on the pet at the time of the treatment. It has no permanence in the animal’s body and therefore is effective for a limited period only. Every time your dog goes out and comes in contact with other animals and with bushes, grass, etc; all of which can be full of fleas. It only takes one tiny flea to start a huge infestation. The manufacturer of Capstar advises to give the pill whenever you spot fleas on the pet.
I usually recommend the use of Capstar as an aid in cases of large flea infestations. In my opinion Comfortis or any other product that has permanence is better.