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 used Frontline Plus for my shih poo and shih tzu. The shih poo has them really bad where her skin is discolored and she scratches constantly. My shih tzu has hard dry patches that I have had to cut off. He has 2 of them. I wanted to know if it’s worth giving them the Capstar now since I’ve given them the Frontline Plus 8 hours ago. Had I investigated first, I would have given them the Capstar first, then FL. I’ve ordered the shampoo and tea tree oil skin relief. Please advise.

  2. Dr. Michael Dym, VMD veterinarianOctober 6, 2012 at 3:15 pm

    Capstar is fine to use now when active adult fleas found on poet. I think the shampoos and topical will help as well. Also try oral chlorphenirmine at dose of 2 to 4 mg twice daily as an antihistamine ot help with allergic reactions.

  3. My cat and dog have fleas, i first applied a topical flea med(cheap brand) Didny work then i bathed them and combed them, i even sprayed my house base boards and furniture with spray a vet reccommended! Still finding fleas!!!! Help! Is it ok to put another med on them like Advantage? It been a week since last med?

  4. Please do not use frontline on your cat, because it might KILL your cat. The main ingredient in frontline is pyrethrin, or pyrethroid compounds. Dogs and some other mammals have a special enzyme that helps them to break this compound down which is why it is safe to use on the dog but it kills the flea. However, cats lack this enzyme and do not break down pyrethrin. If you give a cat this compound they will start to show signs of poisoning, and if you give them too much, they can die! Please check with your vet and see what cat approved flea medications are out there.

  5. Dr. Michael Dym, VMD veterinarianOctober 15, 2012 at 12:51 pm

    Thanks for sharing. I am always for more natural topical flea alternatives such as cedarcide http://www.cedarcide.com or http://www.wondercide.com

  6. Dr. Michael Dym, VMD veterinarianOctober 15, 2012 at 12:55 pm

    I would wait another week and then fine to use advantage. Try oral comfortis or program/capstar from 1800petmeds as alternatives as well. Remember to treat home as well where much of flea life cycle occurs.

  7. I used petarmor 2 weeks ago on my cats and they are still infested with fleas. It is to soon to use frontline?

  8. Dr. Michael Dym, VMD veterinarianOctober 16, 2012 at 4:28 pm

    I dont see a problem using front line now.

  9. Used Frontline Plus for years no problem until this last summer. We had a very mild winter last winter in Northern VA and the fleas this year have been terrible. The vet was having us stay on the Frontline but I was seeing no results. There was no slowdown of flea activity. They were not dying at all even within the first 24-48 hours after application. It seemed like the fleas had really built up an immunity to the Frontline at least in our area. We kept telling the vet and they said they were having a lot of complaints about Frontline working this summer in our area. They just got in this new product they were having good luck with “activyl” by MERCK So far so good. I put one dose on our Pomeranian and after about 8 hours you could see the fleas having problems and after 24 hours most were gone. Nice to see her able to get good sleep again. Too soon to say how well it does after a month and before the next application but I am very hopeful. It is not cheap, almost $100 for 6 applications but that may not be a hole lot more than Frontline if you figure they are usually sold in 3 month packages. I heard that you have to get it from your vet and it’s not available online yet anyway. Will try to update after using for a while longer. Thanks!

  10. Dr. Michael Dym, VMD veterinarianNovember 1, 2012 at 9:44 am

    Thanks for sharing. Will be interesting to see how activyl works long term.

  11. Can comfortis be used with the topical advantix?

  12. Dr. Michael Dym, VMD veterinarianNovember 5, 2012 at 10:46 pm

    You can use these but I think it is too much pesticide for one animal, and would rather you choose one or the other.

  13. Thank you for your response. I had been using Frontline religiously for years but had break through early this fall. I switched to Advantix and treated the environment like crazy and have been giving my dog flea baths each week for about a month. I found fleas on him yesterday. I wondered if treating with a medication having a different mechanism of action from Advantix would help. Fleas are a formidable enemy!!

  14. Dr. Michael Dym, VMD veterinarianNovember 6, 2012 at 6:13 pm

    Perhaps try oral pills such as comfortis or oral program/capstar.

  15. I had a “guest dog” visit for a few weeks and she brought fleas into the house. My home that has been flea free for years now appears to have fleas again. I treated my 5 dogs with Frontline on 11/2 and two of my dogs still have active fleas. I also have Bayer’s Advantix and thought that I would try and treat all of the dogs again today (7 days later) with this product. Must I wait longer than 7 days to treat with the Bayer product?

  16. Dr. Michael Dym, VMD veterinarianNovember 9, 2012 at 12:13 pm

    I would wait another 3-7 days and then apply advantix. Also consider oral products like capstar and comfortis which you can use now from 1800petmeds.

  17. Browsing here because my one cat, we have 3, and 2 dogs seems to be a flea magnet. Used less expensive remedies with minimal success, then switched to Advantage for all the furkids. Big guy still has 2 fleas 24 hours after applying the Advantage. I went so far as to cut his fur prior to application, he has medium fur with a double coat. Fortunately he likes the attention.

    Anyway, I noticed someone suggested giving pets garlic, um, I wouldn’t recommend that. The ASPCA lists it as toxic to both cats and dogs. I know it was once considered a good idea but apparently it causes red blood cell damage so I’d try something else if you want to go natural. I hear borax is good for carpets and furniture, fleas have exoskeletons and it kills them. A long process but eventually works and is non-toxic I’m told. I can’t do it because my one dog is allergic to fleas

  18. Dr. Michael Dym, VMD veterinarianNovember 13, 2012 at 12:28 am

    In 20 years of vet practice I have not seen small amounts of garlic toxic to pets. See book Dr Pitcairns guide to natural health for dogs and cats by Richard Pitcairn, DVM, phd on natural flea control suggestions of which cloves of garlic is one long term successful one.

  19. Okay I wanted to try things out before posting back here again. Comfortis worked for exactly 2 weeks, before I saw little black flea poop on his butt area. I tried some all natural sprays, specifically the one from Vet’s Best, and those didn’t work well either and the herbal mint and clover smell makes me sneeze a lot.
    New idea?

  20. Dr. Michael Dym, VMD veterinarianNovember 13, 2012 at 6:24 pm

    I would try diatomatcious earth topically as natural flea control Also consider oral capstar and program from 1800petmeds.

  21. “look it up…..” NOT everything you read on line is accurate, or even sensible!

  22. Our cat (about 4 yrs old) has fleas (we believe picked up from someone’s yard when my husband visited and brought in on his clothes when he got home).

    We purchased Adams topical, applied it as directed (at the base of his neck pulling the hair back) about 2 weeks ago but our cat still has fleas. I recently became disabled from fibromyalgia & cancer and my husband is unemployed & we can’t afford the expensive Frontline or Advantage treatments, which is why we had to get the Adams since it was 1/2 the price. Do you have any recommendations of how we can help our cat with the fleas? I haven’t noticed any in the house or on us thusfar. We don’t want our cat to get sick & also don’t want it to become a problem in the home with fleas either. We’d appreciate your help & guidance.

  23. Dr. Michael Dym, VMD veterinarianNovember 24, 2012 at 8:06 pm

    Not much I can suggest as cheap alternative. I would try oral capstar and program from 1800petmeds.

  24. Frontline absolutely DOES NOT WORK. I used borax in the den, completely covering the carpet, moved all of the furniture and waited 8 HOURS before vacuuming. BOMBED THE DEN. I had the cats outside of the house in a flea-free home. where they had a flea bath in that flea-free home. Treated them with frontline. Put them into the den. 3 days later, FLEAS who do not seem to care whatsoever about the Frontline Don’t tell me that it’s important to make sure the environment is treated; the entire house had been bombed the week before, AND BORAXED. This was the SECOND TREATMENT. To say that fleas are not evolving resistance is to deny evolution. The longer they delay acknowledging what they know, the larger the settlement will be in the class-action lawsuit. BECAUSE THE THE STRESS IS PAIN & SUFFERING. KEEP YOUR RECEIPTS.

  25. Dr. Michael Dym, VMD veterinarianNovember 28, 2012 at 9:42 am

    Thanks for sharing. I have heard of many stories of front line not working as well as it used to.

Leave a Comment