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Can I combine flea meds after giving my dog expired Comfortis?

Updated On September 23rd, 2025

Pet's info: Dog | Mixed Breed Medium (23 - 60lb) | Female | spayed | 26 lbs

Hi there. My dog has a flea issue. Accidentally gave her expired comfortis last wed. She had a bath Thursday and I got a diff flea med. can I give that to her now since I'm finding more fleas or do I have to wait longer. I obv don't want to give her too much. Also can I use a seresto collar and the oral dose?

3 Answers

Most Helpful Answer

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Answered By Kevin Sanada, DVM

Veterinarian

Published on September 3rd, 2017

Hi, The truth about expiration dates is that they are usually not based on any studies and the drug is likely to be just as effective years after. I can't say for sure, but it's likely that Comfortis will work. However, the fleas should all be dead within 24 hours, so if you are still seeing live ones jumping around, then it likely didn't work well. You can definitely use the flea collar with Comfortis and this may help to rid her of the remaining fleas. I recommend waiting another week after applying the collar to assess if the treatment worked. If you are still seeing fleas crawling around, then you can try a different flea product like Frontline. Avoid any products that contain ivermectin or any other avermectins for at-least 4 weeks after giving the Comfortis - you can check for this by looking at the active ingredients on the package...any name that ends in "-mectin" should be avoided. I hope that helps and Maggie if flea-free soon.

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    Answered By Dr. Macartney, BVet Med, MRCVS

    Veterinarian

    Published on

    I am sorry you are having a difficult time gettin on top of the deal problem. Fleas can be very tricky to control. Because you have recently used a comfortia treatment that was expired I would not advise using any other medication for the time being. It is difficult to know how Maggie's system will react to the experience medication and it is better for her health to not attempt any further medications and this complicate the matter further. Watch for signs of vomiting, dirrhoea, inappetance or changes to thirst or urination which could indicate she is not tolerating the medication well. I believe there most likely outcome is simply that the comfortis will be ineffective as it's past it's use by date. You can switch to the seresto after one month from giving the comfortis. I would advise using either the collar or an oral medication and not the combination. Too much medication can overwhelm Maggie's system and may not be needed. In the meantime, Remember that in addition to treating fleas and ticks on the animal, you also need to treat the pet's environment, indoors and out. Many indoor products contain both an adulticide (permethrins and pyrethrins) and ingredients to kill the eggs and larvae (Nylar ). Examples include Bio Spot® Room Fogger, Bio Spot® Carpet Powder, Bio Spot® Carpet Spray, and Bio Spot® Yard Spray. Fleas actually spend most of their life cycle off of a dog and so treating the home is very important. When using foggers, you need to cover/seal fish tanks, and remove any birds, before using. Vacuum and wipe off counters/eating areas thoroughly after using any fogger. Here is some information on how to treat your home and Maggie to get rid of fleas; https://www.petcoach.co/article/5-tips-to-get-rid-of-fleas/ I hope that is helpful and please ask as many more questions as you may have on this topic. I am here to help!

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    Answered By Vanessa Yeager DVM MPH

    Veterinarian

    Published on

    Hello and thank you for your question on Petco Pet Education Center, formerly Petcoach! Yes you can use a Seresto collar or a topical flea treatment. I wouldn't use both. I don't want to overload her system. In case the comfortis was somehow still effective even after the expiration, I wouldn't give her another oral flea medication, but a topical would be okay: either topical or collar. I hope this has helped answer your question! Best of luck to you and Maggie!

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    1Pet Parents found this answer helpful

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