Bayer K9 Advantix II 4 Dose Flea And Tick Prevention & Treatment for Medium Dogs, 11-20 Lbs. This veterinarian-recommended topical formula kills fleas within 12 hours through contact, eliminating the need for painful bites. Waterproof after 24 hours, it provides continuous protection against fleas, ticks, and mosquitoes for up to 30 days, even after bathing or swimming. Contains four 1-month applications.