Capstar has the active ingredient nitenpyram, a substance from the neonicotinoids group. This group is modeled after natural nicotine. It is one of the safest medication against fleas. It works by causing hyper-excitability prior to the death of fleas. It is absorbed rapidly and the maximal concentration in blood is found after an hour of administration. It works fast, killing the fleas within 3 to 4 hours. It is eliminated rapidly as well, around 90% within 24 to 48 hours, mainly through urine. The safety studies made prior to approval with overdoses and daily long term treatments have not produced any side effects. The only disadvantage is that it kills only adult fleas, it does not break their life cycle. But it can be administered more often then the other flea medication. Fleas life cycle can take from two weeks to months depending on the environmental temperature. If you give one tablet every ten days I think that should be enough. This product kills only the fleas found on the dog at the point in time after administration, it does not have permanence like the other products. So your dog is flea free until it catches them again.