Eliminating fleas on your pet is easy with Capstar (nitenpyram) because CAPSTAR provides fast flea relief for your dog or cat. In fact, it starts working within 30 minutes to kill adult fleas. You will literally see fleas fall out of your pet! Protecting your pet against fleas is an important part of keeping your pet healthy and happy. Fleas are the most common external parasite found on dogs and cats. (source: petsandparasites.org). Fleas can not only make your pet uncomfortable, but they can also carry other diseases or tapeworms. In addition, if left untreated, some fleas on your pet can quickly lead to a large scale infestation in your home.