K9 Advantix II Extra Large Dog is a veterinarian-recommended monthly topical treatment that protects dogs weighing over 55 lbs from fleas, ticks, mosquitoes, biting flies, and lice. This Costco pack includes 8 monthly doses, providing an 8-month supply of comprehensive parasite protection. Made by Elanco, each 4.0 mL tube is applied directly to the skin along the back.

The formula combines three active ingredients — imidacloprid (8.8%), permethrin (44.0%), and pyriproxyfen (0.44%) — to kill parasites on contact without requiring a bite. It kills fleas at all life cycle stages including eggs, larvae, and adults, and begins working within 12 hours of application. The waterproof formula remains effective after bathing, swimming, or exposure to rain once the application site has dried (approximately 24 hours). A single tube should be applied in 3–4 spots along the back to prevent run-off.

Safe for dogs and puppies 7 weeks of age or older weighing over 55 lbs. Never use on cats — permethrin is highly toxic to felines. Keep children away from treated dogs until the application site is fully dry. Avoid allowing treated dogs to enter surface water for 48 hours after application. Monitor for skin irritation at the application site; consult a veterinarian if reactions persist beyond 3 days.