What to do when pet’s flea medication stops working

 To eliminate a flea infestation, it takes patience treating your pet and your environment.

All too often, a pet owner will come in and share their experience in which he or she regularly applies topical flea prevention, yet is frustrated that after several treatments they are still seeing fleas. There are several plausible explanations for persistent flea infestations which may have nothing to do with lack of efficacy of these products.

Apply flea medication properly for maximum effectiveness

First, I ensure the pet owner is correctly applying the flea medication to his or her pet. It is important to completely part the hair and apply the product directly to the skin so that proper skin and hair follicle distribution can occur. This is something that can be somewhat of a challenge for thick haired pets; however, the pet medication will not work properly if only the hair follicles receive the medication – it must be applied to the skin. Next, it’s important to properly follow product label directions, which may vary depending on the size of your pet. For instance, for large dogs, Advantage II requires the product to be applied on multiple spots down the pet’s back.

While it is tempting to try and save money by using only portions of products labeled for larger pets on smaller animals, it’s a process such as this that can lead to product inefficiency.

Ensure your home and yard are treated 

Another reason for products not working is by not treating your home and yard, where in some cases 80% of the flea life cycle may occur. Read how to control fleas indoors and outdoors.

In cases of heavy flea infestations, some home products such as Advantage Carpet and Upholstery Spray kills fleas and ticks quickly and continues to kill fleas for two weeks. In spite of recent discussion in the veterinary literature, the development of widespread flea resistance is still not believed to be a major factor to clients still finding fleas on their pets.

Consider switching to oral flea medications

The newer oral flea medications are becoming very popular and with good reason — they’re even more effective than topical treatments at killing adult fleas and keeping your pet flea-free. Plus, with an oral flea treatment, you eliminate the mess of topical flea treatments and the worry about whether you’ve applied the product properly.

Have you been battling a flea infestation in your home? What are some of the ways in which you have been trying to get rid of them? 

Have pet health questions? For any medical concerns, we always recommend you consult your veterinarian. However, for non-emergency questions, you can contact Dr. Dym directly using our Ask the Vet form.

Related Posts


  1. I have a 16 yo indoor female cat who is infested again with fleas. I’ve been using Bio every month for 3 months washed everything possible flea combed bathed in Dawn almost weekly and treated indoor enviornment plus vacuumed. No good results. Cannot kill cycles or mature fleas!! My cat is overweight and may be diabetic. I’m afraid vet’s meds may be too toxic. Beside myself…not sure what to do…this cat is my life and don’t want to lose her!!

  2. Hi Carole and thank you for your question. For any medical concerns, we always recommend you consult your veterinarian. However, for non-emergency questions, you can contact Dr. Dym directly using our Ask the Vet form. We hope your kitty is flea-free soon!
    ~ Abby, PetMeds Pro

  3. I have a10 month old Peekapoo puppy. I applied Advantix 2 which worked great on my previous dog. It worked great this time for about 2 weeks and now she is miserable with fleas. What can I do since the Advantix is a monthly treatment?? I bathed her in Dawn but that’s only good for a couple of days and I don’t want to dry out her skin by washing too often. Please help!!

  4. Hi Joy. We’re sorry to hear your pup is troubled by fleas. Here’s what Bayer has to say about K9 Advantix:

    “Although K9 Advantix® II kills fleas on your dog, there may still be fleas in your dog’s environment that have since jumped on after treatment. Luckily, with K9 Advantix® II, new fleas are killed within 2 hours with protection against further infestation for at least 4 weeks. As fleas die they are no longer able to stay hidden against your dog’s skin, and therefore you may also be seeing dying fleas coming to the surface of your dog’s fur coat.”

    We recommend treating the environment with a room spray or fogger. In the meantime, ask your vet about using an oral product such as Capstar which will immediately kill any remaining adult fleas, although the effect will only last for 24 hours.
    ~ Abby, PetMeds Pro

  5. I have a nearly seven year old cat named Genevieve. We got her from the shelter over 8 months ago and when we took her in for her first check up she had some hot spots on her skin. Vet didn’t see it as much of a problem, but we got recommended that we keep her on flea treatment in case it was a flea allergy and to change her food to grain free in case it was a food allergy. She is indoor only.
    For the past two months we have found fleas on her and have tried changing her flea meds (she was on Petarmor, then switched to Frontline, now switched to Advantage 2). Each time the fleas disappear for a while, i strip the covers off our couches as well as bed, spray advantage indoor home spray on nearly every surface, and yet still the fleas come back 5-6 days later. We have been careful to wait the full 7-30 days as the instructions on the box specify (Advantage says for infestations, a flea treatment every 7 days can be helpful, while Petarmor and Frontline said 30 days minimum between dosages). We gave her a flea bath between switching from Petarmor and Frontline, and that worked a while as well. Every two days I comb through her fur with a flea comb and drown the live fleas in a liquid dish detergent/water mix. Still, fleas.
    This case of fleas has aggravated her skin so much that she has many hot spots, she itches herself until she bleeds (we have since put a cone on her to prevent such damaging scratching and biting), and she has been losing fur. We took her to the vet before she started losing fur and the vet recommended the advantage spray for the home and advantage 2 flea treatment for cats over 9 lbs.
    Is there anything else further that I could be doing? Not sure how my apartment complex would respond to us flea bombing the place, but if need be I could do so.

Leave a Comment