Capstar (nitenpyram) is a veterinary medicine used to treat flea infestations in cats and dogs. It is a fast-acting oral tablet that kills adult fleas. Capstar is effective within 30 minutes of administration and eliminates over 90% of adult fleas within a few hours. It is often used as a quick-relief treatment during active flea infestations or in conjunction with other flea prevention methods. Safe for dogs weighing 2 pounds or greater, and 4 weeks of age and older..