You have Frontline stocked and religiously give it to your dog every month. He’s protected from fleas and ticks, right? Well, maybe.
Topical flea medicines like Frontline or K9 Advantix lose their effectiveness throughout the month, especially if your pup has had a bath or goes for a swim during that time. So by week three or four, the effectiveness could only be at 50 percent or less, which is a problem for dogs who are flea allergic.
Bay Area Veterinary Dermatologist Dr. Nicole Eckholm says your dog will generally be okay if you give a topical flea preventative once a month but if you dog is flea allergic, it might be a good idea to give it every three weeks.