Trifexis is a monthly chewable tablet for dogs that kills fleas, prevents heartworm disease and treats and controls adult hookworm, roundworm and whipworm infections. Trifexis combines two active ingredients to provide protection for your dog against three kinds of dangerous parasites. Trifexis is beef-flavored, so you can offer it as a treat. Milbemycin oxime is used as a heartworm preventive. It kills the immature form of the heartworm (Dirofilaria immitis), which is transmitted by a mosquito. Milbemycin also kills adult hookworms, roundworms and whipworms. The spinosad in Trifexis prevents and controls flea infestations by killing adult fleas. Trifexis is for use in dogs and puppies 8 weeks of age or older and 5 lbs of body weight or greater.