Capstar kills all adult fleas on a dog...for 24 hours. It is meant as a 1 time flea treatment to give time for the slower acting topicals to take effect. (The company's actually purpose was to use it as a supplement with Sentinel. Sentinel inhibits flea reproduction, then the Capstar kills off the adult fleas. With all the adult fleas gone and eggs unable to grow and larvae starving...no more fleas!)
We use it all the time to "flea bomb" dogs that come into work and are going to board/get groomed. But without a follow up flea prevention, as long as the dog is still exposed to fleas in the environment...he'll be crawling in fleas the next day.