Stronghold Plus (selamectin & sarolaner) is sed to treat parasitic infections in cats. It is a spot-on solution applied to the skin that works by killing or paralyzing parasites such as fleas, ticks, mites, biting lice, ear mites, heartworms, roundworms and hookworms. Affects the nervous system of parasites, leading to their paralysis or death. Indicated for cats with, or at risk of, mixed parasitic infestations. Contains Sarolaner, a member of the isoxazoline class.