Each package of K9 Advantix for Dogs lasts 4 to 6 months (One vial per month) * Kills 98%-100% of fleas within 12 hours - helpful in dogs with Flea Allergy Dermatitis * Protects against deadly Lyme Disease, spread by ticks * Repels and kills mosquitos, carriers of dangerous West Nile Virus * Water-resistant, easy to apply formula stays on in baths or in the rain