Vomiting, lethargy, diarrhea and appetite loss are some possible side effects of Comfortis in both cats and dogs, according to Elanco, the manufacturer of Comfortis. Cats may also experience weight loss and diarrhea when taking Comfortis, while dogs may suffer lack of coordination, itching, trembling, excessive salivation and seizures. Incidents of adverse effects of Comfortis in dogs decrease with subsequent dosing, indicates Drugs.com.
Dogs who take Comfortis along with ivermectin may experience trembling or twitching, excessive salivation, seizures, lack of muscle control, dilated pupils, blindness and disorientation, warns Elanco. The company advises caution when using ivermectin concomitantly with Comfortis in cats. Ivermectin is an antiparasitic medication that prevents heartworm and treats conditions that include mange, notes petMD.
Comfortis is the brand name of spinosad, an oral medication that cats and dogs take monthly to kill fleas and prevent flea infestations, explains Elanco. It is safe for use in dogs and puppies over 14 weeks old who weigh at least 3.3 pounds and in cats and kittens over 14 weeks old who weigh more than 2 pounds. It is unknown if Comfortis is safe for cats and dogs who are breeding, pregnant or lactating. Because Comfortis contains pork, pets that are allergic to pork should use a different flea preventative.