Can Fleas Become Resistant To Traditional Flea Medicine?

Here’s a scenario to consider: you typically experience flea outbreaks around the spring/summer season, so you apply FrontLine Plus to protect your dog against these blood-sucking parasites. Normally, FrontLine does an excellent job at eliminating the flea infestation, allowing your dog to live without the nuissance of flea bites. But for some reason the medicine has stopped working, and the flea population is spiraling out of control.

Fleas May Develop a Resistance To Treatment/Preventative Medicines

So, can fleas really become resistant to a particular drug, such as Fipronil — the active ingredient found in FrontLine Plus and several other traditional flea treatment/preventative medicines? There’s very little research regarding this topic, but the general consensus among veterinarians is that yes, fleas can develop a resistance or even immunity to certain types of flea medicines.

Over time and with constant exposure to flea preventatives, fleas will eventually develop some degree of resistance to the product. This resistance is passed on generation to generation among the fleas, rendering the product less and less effective. This may indeed be happening with Frontline. It is for this reason that I have stopped recommending Frontline for flea prevention in my dog and cat patients,” wrote Jeff Kahler, a professional veterinarian working out of Modesto, California.

Granted, there are some veterinarians who believe this is merely a myth — that fleas do not develop a resistance to drugs; however, most will agree that it’s a real phenomenon.

Tips To Prevent Drug-Resistance In Fleas

  • Stay up to date with your pet’s flea medicine, reapplying it when instructed by the product manufacturer (usually 30 days for FrontLine Plus and other products containing Fipronil).
  • If you believe fleas are becoming resistant to a particular medicine, try switching to a different product. Rather than reapplying FrontLine Plus, for instance, perhaps you can try Advantage. As long as it has a different active ingredient, it should work.
  • Make sure you apply the correct dosage of flea medicine to your pets. Using the wrong size formula (e.g. the small size formula for a large dog) may increase the risk of resistance while offering your pet minimal protection.

It only makes sense for fleas to develop a resistance to drugs they are frequently exposed to. This is a common phenomenon that occurs in thousands of animals, and fleas are no exception. When they are exposed to small amounts of a chemical over a long period of time, they will adapt and grow used to it; thus, reducing its overall effectiveness.