Sentinel is a pet medication that treats fleas, heartworm, and intestinal worms. Pet medications are prescription and over-the-counter medicines for dogs, cats, and other animals. They treat animal-only conditions and those also found in humans, and come in forms and dosages specifically for pets. Get Sentinel for as low as $72.99, save up to 80% off the average retail price for the most common version, by using a GoodRx coupon.