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.

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  1. WOW! That is interesting! Finding MANY folks in the south saying frontline plus does not work . Now i know why.

  2. I live in Florida now, we just recently moved from NY, I didn’t know the sand fleas here are rampant, I have used the DE on my lawn and it has dried out the grass terribly that my dog will not even go there anymore, the grass is like hay now, her paws got very dry, so be careful when putting it on your pet as it is a very drying powder , but I have heard the only pill that really works here is Trifexis by prescription by a vet. I hope it works the topical products do not seem to work down here.

  3. Trifexis is certainly excellent flea control product, although some pets can have digestive upset from it so best given with meal, and you will need written script from local vet. If you like natural products, also see the lemon peel protocol in book Dr Pitcairns guide To Natural Health for Dogs And CAts.

  4. I’ve had my little dog since last June and never saw any fleas whatsoever till yesterday. I swear one minute, none and then several and she is miserable and I am scared. I’ve never had a flea infestation with any of my dogs so do not understand this. She doesn’t even go outside except on the screened-patio. I give her Trifexis every 4 weeks without fail and ensure she swallows it so I simply do not understand this. Can a dog develop an immunity to the medication? I bought those foggers and activated them today and left for 2 1/2 hours; do not detect any odor upon return. I also bought some anti-itch wipes and used them on her; she seemed to get a little relief. It is very frustrating to me a she is so anxiety-filled at this turn of events that she only wants to sit on my lap and whine, thereby keeping me from getting much done. Even in the van ride today to get away, she had to sit on my lap and fuss. It was most disconcerting. Any advice out there? I am taking her to the vet on Monday but would appreciate any input from out there too! Thanks for listening. Janine Johnson

  5. HI Janine. Sorry about the current issue. Perhaps she just exposed to fleas suddenly and that if trifexis being given regularly that within hours the problem will resolve. Other possibility is that there is problem in home environment which you may want to address with products like knockout for fleas from 1800petmeds, or flea busters which you can look up on line. Also professional exterminator service also sometimes needed, as 90 percent of flea life cycle occurs in home. Perhaps one of other pets in home has bought fleas in so I would check that as well. From my experience and from what I have heard, trifexis drug resistance has not been seen as far as I know

  6. I have owned two to three dogs at a time and always one cat ( that always “thinks” he’s a dog, that’s why only one cat always…… Well, it’s a different world now I guess and I’ve never had fleas nor my animals in 25 years,.
    Well, now everything I buy that always used to work has completely stopped working and within a week my home is infested. My vet said the fleas now are immune to all that worked before….. Please help!

  7. HI Alicia. I would make sure you are treating ALL of the animals in the home, as sometimes, clients will not treat the animals that are itchy or have skin lesions, but they may be carrying immature larvae and/or eggs on the coat, without causing an allergic reaction in a particular pet, but will still infest the environment and/or keep infestation going. I would consider nexguard for the dogs and comfortis for the cats, or the cheristin collar. It is also important to treat the home environment in the yard and/or indoor home, as much of the flea life cycle still occurs in the home. I dont agree with your vet that modern and new products like this are no longer effective. Treat all of the animals. Treat the home!!!

  8. None of the inside treatments will work if you also don’t treat your yard every 6 months. I am having a hard time with flea control recently, I bought the Comfortis, which is really expensive, but it is a huge pill and the cats won’t ingest it. I have tried making it into a powder and hiding it in their food, but they won’t eat the food if I do that. I have tried advantage II and it just doesn’t work anymore. But we didn’t use the pellets on the grass, so we are giving that a try. Sprayed the house. Applied Advantag II, and treated the yard. We have tile, so vacuuming and washing the floors should help too. I wish you luck. Try combing your cat and drowning the fleas in dawn and water and for sure treat the yard.

  9. Excellent points Grace. Treating the ENTIRE environment when one has a flea infestation is very important, as most of the flea life cycle does occur in the home or yard. This does explain, while some people dont get adequate flea control relief by just treating their pets with the newer and certainly effective prescription products available. Many years ago, we always stressed treating the home as well, which seems to have been forgotten often with many vets today with the newer and more effective generation of products used on pets.

  10. I have treated my home and yard. Treated the 4 dogs with biospot. Today I noticed on one of the dogs they fleas have moved to his head. I applied it between their shoulders to the nase of their tails. Wehave been fighting this problem for over 2 months.

  11. Hi. I used Frontline on my 2 cats on 6/14 and 6/15. It has done nothing to help, I am pretty sure I applied correctly. I purchased Advantage and my question is…. ..When is it safe to reapply? I would like to do it today 7/18 but worry about negative side effects. Do you think enough time has passed (32-33 days) ?? Thank you

  12. Hi Tami. Also Kim. As for Tami’s question, I would consider getting script for oral comfortis or Nexguard or Simparica from your local vet to fill at 1800petmeds. You may need additional products. Also make sure you treat home with good product as well such as with Knockout as much of flea life cycle occurs in home. As for Kim’s question beolow Tami’s, I would have no problem applying the advantage now

  13. I need some advise/help please. Around thanksgiving my poor boy was infested with fleas. I immediately began treating the issue not only with him but my environment. Three months of treatments, from baths to his topical medication, oral medication, washing his bedding weekly and his surrounding daily I was having no such luck. These buggers were still present. Feeling like i had exhausted every option, his vet recommended the Seresto Flea collar and within two weeks I was finally able to take a breath and see some light at the end of the tunnel.

    Fast forward to two weeks ago Monday, my husband noticed my poor dog was covered again. We immediately treated him with CAPSTAR and kept him in the garage overnight. The following day he received a flea bath, treated everything and on Friday of this past week put a brand new Flea Collar(we assumed his old one ran its course).

    5 days later poor guy still has them on him. NOT covered but enough to have my skin crawl and be on alert. He’s tired of being picked at and secluded to a section of the house. I have spoken to other dog owners who fortunately for them, have not encountered any issue with FLEAS and with that being said are no help. I don’t know what I am doing wrong, or if its simply the breed of my dog(he’s a husky). Desperate not knowing what else to do,

    I reached out to his vet who suggested using an oral monthly medication alongside his flea collars as sometimes they do work as well on bigger dogs. They also advised to treat my environment as that will also play into effect.

    How do i prevent this from continuously occurring? I do not own any carpets, all my floors are hardwood and tile and i vacuum my entire house everyday. Its truly exhausting. I am 7 months pregnant which makes this whole process that much more difficult and I fear that once the baby is born i will not be able to be as attentive as i am now.

    I did invest in a bottle of Richard’s Organic Flea & Tick prevention. I was told this product works great and acts as a “bug repellent” for fleas. which I have applied directly to his coat.

    My poor boy is miserable and tired of being checked everyday.

    Any and all feedback would be greatly appreciated.

  14. Hi VAl. Perhaps you got a bad or defective seresto flea collar as does not make sense that it would not work as well the second time around. I would call company and speak with customer service rep or vet support staff to get input. In mean time you can use oral capstar once daily for several days, as well as try and treat home as you have been doing as well as dont forget about yard as well, as most of flea life cycle still occurs in home

  15. My dog has been on Advantix since she was a pup (she’s 5 years old), and my cats have always been on Advantage. We just moved 4 months ago, and now my pets have fleas. They’ve never missed a dose. We’ve treated the yard and used diggers in the house. We had an exterminator come out. I switched to Frontline. We STILL have a major infestation! I was a CVT for 18 years, so yes, I’m applying it correctly. They get Capstar, which helps, but it only kills the adult fleas.
    There is no way any vet can convince me that Advantix and Frontline still work when my dog and cats were on it and still ended up with fleas. The home i bought was vacant for nearly 3 years (foreclosure), and we remodeled down to the studs. It didn’t have carpet, the flooring and baseboards were all replaced, even the subfloor. Even if they were in the yard, that was treated and my pets were on a preventative, so we shouldn’t have become infested in the first place. Before I left veterinary medicine to be a stay-at-home mom last fall, I had a lot of clients complain that Frontline, Advantix, and Advantage were no longer working. I used to tell them the same thing. They work, you just gave to use them correctly and treat the environment. Now I know that’s the problem. It’s the fleas that are resistant.
    (I’m in southwestern Illinois, where it seems to be a common occurrence that fleas are resistant to these products)

  16. Edit for my above comment:
    We used foggers, not “diggers”. It seems my phone goes insane with autocorrect.

  17. Hi Natalie. I have also seen occasional problems with resistance(in clients who are also treating home as well) with some of the older flea products. I would change over to some of the newer tablet alternatives, such as Nexguard or Simparica

  18. My cats are resistant to advantage11 revolution and now cheristin. I used all of them for about 3 years each. I have borax on my carpets now I let it stay about 2 days then vacuumed. Washed all bedding more than once. I Iive in Florida. I bought comfortis it made two of my cats sick one of them for days. The rest of them were ok and the fleas died. Guess I will continue to battle fleas all summer and winter. Fleas coming back after two weeks. I just wish they were not immune to the medicines I used to give them. They worked so well. I could put it on them and it would last well over a month. I have 9 cats. I still have a 6 pack of comfortis but don’t think I will use it. I have read too many bad reviews about cats and dogs dying. Two of my cats were sick.

  19. HI Lisa. Sorry to hear of your awful battle with fleas. I find that in most situations like you are describing with so many cats as you have, that the preventatives are not working on at least one or a few cats thus accounting for the re infestations. Flea comb all cats regularly to see which ones might be the offenders, as those particular cats may need alternative flea control products from your vet. Does not mean that a particular single product does not work. May not work in a few of the animals due those animals having an immune system that does not allow product to work as well or makes them more susceptible in spite of the appropriate labeled use of the product. In other words, you may need a combination of products in the house at one time. NOT just one product for all of the cats. Also make sure you are treating the home and yard as well, as much of flea life cycle occurs in home. Perhaps consider exterminator and/or product like flea busters which you can find on line and is based in Florida. Good luck with frustrating situation

  20. I have 2 cats and a dog. My larger cat has fleas and flea allergies. This occurred w/in the past 12 months. I’ve had him 9 years and he’s never had fleas before. I treat them all with Front Line and yes, 47 years old and cats all my life… I know how wo apply it. The dog and smaller cat have zero fleas. My poor big cat can’t seem to get them off him. I refuse to believe “fleas are in you home, treat your home”. When I don’t see any evidence of fleas him my home and I have two other pets that are not having the issues with the fleas. I don’t think it’s necessarily a product issue since it seems to work fine on the other animals, but we’ve been using frontline for some time and this is a whole new issue for me and the cat.

    I find flea dirt and usually 3 or 4 fleas when using a flea comb… which is also confusing because I have experienced some bad infestations in my teenage years where they were jumping on humans and you could see them on the pets. We had to use flea bombs/foggers. I’m at the point where I’m going to treat my current home, but with hardwood floors through out and finding no evidence of them in the furniture… I don’t know how he has them and the others do not. Any thoughts?

  21. What if my dog moved and some of the medicine ran down her fur? Will it still work and do I need to wipe it off?

  22. Hi Tom. You need to treat ALL surfaces including your hard word floors(i.e steam clean), etc as fleas can live on baseboard, cracks in floors, etc. You also need to treat ALL bedding and ALL of the animals, even if you dont see any fleas on the other pets, as not every pet is flea allergic or flea susceptible but they can be a resource and non symptomatic carrier of flea eggs, etc.

  23. HI Tammy. I would not worry about it. DONT reapply flea topical medication until it is next labelled in drug packaging. Let’s wait and see if enough got absorbed into hair follicles to be effective with flea control over next 10 to 14 days.

  24. My cat got fleas in the last 2 weeks. He has never had them before, and has longer hair. Tonight I found a bunch of spots and a big place where he has almost scratched his fur off. I bought Sentry PurrScriptions at PetSmart tonight, about all they had besides Frontline and Advantage. I bought the Sentry for cost as I just wanted it for now. I am going to research more for further months. I also bought a flea and tick wipe with geragenia and peppermint that I rub all over him.
    I intend to buy the borax for the carpets. But then I read a bunch of bad reviews about this insecticide used in the Sentry. I used to use flea collars and they worked great. So what are your thoughts? Do I quarantine him in his carrier? What if this doesn’t work to kill all these eggs and such? I am so sorry that I didn’t notice this? My cat sitter said he gave him a dose of something while I was away and he didn’t go outside, but he sure has a bunch of these spots.

  25. Hi Carla 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 feeling better soon!
    ~ Abby, PetMeds Pro

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