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. Dr. Michael Dym, VMD veterinarianJuly 13, 2012 at 3:50 pm

    Your veterinarian’s recommendations are good ones. Preventic collar is good for tick control.

  2. Dr. Michael Dym, VMD veterinarianJuly 13, 2012 at 3:52 pm

    I would wait 4 to 5 days and use a better product such as canine advantage or front line.

  3. Hi Dr. Dym,
    I have a little jack russell/cairn terrier who is primarily white and a flea magnet! I fronlined him just two weeks ago, and today I pulled about four fleas off of him and he is an itchy mess (poor guy). I appreciate your advice about treating the house; that makes sense and we will do that. My question, is whether you should treat your yard – he is very low to the ground and loves to just roll around in the grass. We’ll take care of the inside, but what to do with the outside??
    Thank you,

  4. Dr. Michael Dym, VMD veterinarianJuly 21, 2012 at 2:58 pm

    There are flea killing yard and kennel sprays that you can look into on line or from local garden store.

  5. Hi,
    I am the proud owner of a 1 year old adopted boston terrier. After using frontline, we obtained fleas. We treated the house with bombing, Dia. earth+salt+borax, we have fed him garlic, and we finally had to take him to the vet. After a pricey visit i was sent some with steroids, histamines, and simplegaurd. A few days later, I was flea combing, found a flea. I called the vet, returned my 6 month supply of simplegaurd in exchange for Certifix. I applied immediately (vet said it was ok) and the black dots got less and less during flea combing. my flea water traps all over the house were coming up clean for 2 plus weeks. I thought, Yippie! i found the trick, lets enjoy summer….WRONG. I went back to buy certifix 4 days earlier than the 30 days, put it on the next day, and whamo, in the past 24 hours got 3 fleas off the dog. i flea water trapped the house and all clean so i know im not infested…yet? But my poor boston is losing hair. I am so frustrated on trying to find something that works for my VERY active puppy. he’s unhappy because he has a decrease in outdoor time. he stays up all night itching. I dont know what to do to help my poor lil balding boston (he clearly has an allergy to them, they need to stay off!). I want to wrap him in plastic wrap to go out peepee! Am i unrealistic to believe in the replant aspect of these medications? I have a call into the vet. Any suggests are helpful!

  6. Ps.
    I have also treated the yard for two months with chemicals that says they kill for 3 months. I am trying : (

  7. I invested in a bag less vacuum cleaner. I empty it every day after a vacuum and wash the filters weekly. I have also heard moth balls in the bag will help. I am trying that now.

  8. Dr. Michael Dym, VMD veterinarianJuly 24, 2012 at 6:12 pm

    Hope it works for you. Consider great product from flea busters for home which you can find on line

  9. Dr. Michael Dym, VMD veterinarianJuly 24, 2012 at 6:12 pm

    Sounds like you are doing best you can.

  10. Dr. Michael Dym, VMD veterinarianJuly 24, 2012 at 6:13 pm

    MAy want to ask vet for a supply of capstar orally for quick kill of adult fleas and/or consider other products like comfortis from 1800petmeds.

  11. I had 2 Maine Coon cats, one 7yrs old and the other 15yrs old. After using Pet Armor for 3 months the cats had become very sick and lost their hair on the backs of their legs, both died within 3 days of each other. This is the only thing that could of killed them nothing else had changed in their world. I am so sad loosing my babies. The 15yr old had been with me since he was 8 weeks old, and I had had the 7 yr old for 6 yrs. My heart is broken and I will never use Pet Armor or 1800petmed again.

  12. Dr. Michael Dym, VMD veterinarianJuly 26, 2012 at 1:36 pm

    I am sorry for the loss of your cats. Any topical pesticide applied to our animals does have the potential for causing severe reactions on rare occasions.

  13. are you for real right now?how can you blame advantage ?this product works for 99% of all other users (including myself)but it dont work on JUST YOUR DOG ?and maybe a couple others. come on take some responsability for your own stuff. advantage didnt give you the flea problem and doesnt owe you ANY explanation on why it didnt work for you. its lazy ppl who want to drop a few drops of advantage on their pet and then throw out a few carpets (instead of just cleaning them)and then sit on their butts waiting for MAGIC to happen! and then WOW still have fleas!!! why ???its all advantages fault!! wahh wahh! vaccume,vaccume,vaccume,for at least 3wks twice a day . clean filter outside each and every time you vaccume. clean bedding every three days (pets, also ppls,and couch covers etc.) you must clean under couches,hutches,beds,and throw diatomaceous earth (food grade)in all areas that vaccume cant reach. throw some on floors then vaccume/sweep it up ,also put it right on your pet. AND I PROMISE YOU WILL NOT HAVE FLEASE!!! it takes alotta hard work to get rid of fleas .advantage alone wont do the trick .nor will a one day cleaning of your house.you have to do it at least the length of the fleas life cycle.

  14. Dr. Michael Dym, VMD veterinarianAugust 1, 2012 at 12:54 pm

    Thanks fo rsharing your thoughts.

  15. We use Frontline Spray on our min schnauzer Hannah. She is Flea and Tick Free even though we live 0n a mountain with deep woods. Hannah is 8 years old. Before Hannah we had a dalmatian and a cat which we used frontline spray on both of them all their lives, dalmation 15 years and cat was 17 when they passed, but they lived flea and tick free all their lives. No other product works like the frontline SPRAY. NONE.

  16. Dr. Michael Dym, VMD veterinarianAugust 6, 2012 at 6:37 pm

    Thanks for sharing your experiences. Glad that front line is working for you.

  17. Hannah’s Mom again, just want to clarify it is frontline SPRAY that works for us, not the dose you dab on ? I hear that does not work. We only use the Spray and it keeps fleas and ticks off our pets and out of our home. Even if our dog is around other dogs that have fleas and tick she does not get them. It instantly kills them and prevents them from our pets and our home.

  18. My cat has diabetes and is on Pro Zinc insulin twice a day. She does not go outside but our dog does. I didnt want to put any kind of flea treatment on her, because I didnt put any flea treatment on her she did get fleas and it actually made her diabetes worse where we had to have her insulin increased. I have been putting frontline on her since with no problems. My vet recommended it, even with her being diabetic. Hope this helps!

  19. Dr. Michael Dym, VMD veterinarianAugust 7, 2012 at 3:52 pm

    Thanks for sharing. Sometimes in diabetic animals I will suggest more natural flea prevention such as http://www.wondercide.com or http://www.cedarcide.com

  20. Fleas can drive the owner and Pet insane I do understand . I have A Shep/Irish Setter mix male he weighs between 60 and 65lbs . We bathe him weekly adding A little tea tree oil to his bath and also we use Four Paws Brewer’s yeast with Garlic daily Our Big Boy takes 6 tablets with A little of the canned cheese also he takes fish oil tablets daily (loves them) I live in Middle Ga where fleas can be nasty !! But , doing what we have has worked just just fine no fleas at all . He is an inside doggy we dont allow him to stay outdoors except to use potty and get his excerise . I don’t see how garlic is A toxin to dogs if it’s sold for them .. BEST OF LUCK TO EVERYONE .. Look up the uses of tea tree oil 😉

  21. Dr Dym, how much time should I wait before trying a Fipronil product on my 8 year old dog after using tetrachlorvinphos product. we also have been using a permathrin house spray. I am concerned about too much and too many pesticides.

  22. Dr. Michael Dym, VMD veterinarianAugust 14, 2012 at 6:49 pm

    Thanks for sharing. I have not seen any toxicity in my experience of using fresh cloves of garlic to meals of my holistic clients. Brewers yeast and garlic also helpful in some cases. I also find natural products like wondercide and cedarcide useful as well http://www.wondercide.com and http://www.cedarcide.com

  23. Dr. Michael Dym, VMD veterinarianAugust 14, 2012 at 6:50 pm

    I would wait at least 2 weeks before using Fipronil after the first product.

  24. I am taking the opportunity to \bomb\ the house while the kids are away for three days. I know I have to keep the dogs and cat out of the house for several hours. I want to bath the dogs with Adams flea bath, which works great, but can I use capstar at the same time? Should I use it before I fog the house or should I follow up with it after the bath?

  25. Dr. Michael Dym, VMD veterinarianAugust 16, 2012 at 2:43 pm

    You can try the capstar at any time for quick kill of adult fleas. Does not matter if at time of fogging or bath, etc

Leave a Comment