Yes, it is generally safe to use Frontline and Capstar together. Frontline is a topical flea and ticks preventative medication applied to your dog's skin, while Capstar is an oral medication that works quickly to kill adult fleas. Using both medicines can be an effective way to quickly kill fleas and prevent infestations. However, it is important to follow the dosage instructions provided by your veterinarian or on the product labels and to only use medications specifically formulated for dogs.