Capstar is approved for use in cats and dogs and is available through veterinarians. Capstar is a tablet that kills fleas and does it very quickly. It has no residual action and is useful if you want to quickly eliminate a new flea infestation before using a long term preventive. Capstar contains Nitenpyram, a compound that interferes with the fleas nerve transmission. Within 30 minutes you will literally see fleas falling off your pet. Your pet will scratch initially - this is temporary and is a reaction to the fleas falling off, not to Capstar. Capstar is remarkably effective, whilst gentle on your pet. It does not accumulate and leaves your pet's body within 24 - 48 hours.