Seresto Vs K9 Advantix II: What The Woof Is the Difference?

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seresto vs advantix

Coming into the Winter season we tend to stop thinking about flea and tick control and for the colder parts of the world these parasites all but disappear.

In the warmer or more temperate climates though, fleas still thrive through the winter so it’s not a time to slouch in the war against parasites.

With so many products available it can be difficult to choose one, that’s why here at FluentWoof we’ve done some of the hard work for you with this Seresto vs K9 Advantix II review.

What Do Seresto and K9 Advantix II do?

What Do Seresto and K9 Advantix II do

Both Seresto and K9 Advantix II target external parasites including fleas, ticks, and lice with K9 Advantix II also killing mosquitoes and biting flies while Seresto collars can also treat infestations with sarcoptic mange.

Both of these products are produced by Bayer, a well established and trusted company in pet health.  

Seresto For Dogs Review

Launched onto the animal health scene in 2013, Seresto collars were completely novel methods of treating and preventing external parasites in pooches. Let’s take a deeper dive into the key points of this product:


Seresto collar is applied as a simple plastic collar that you fit around your pet’s neck just as you would their restraint collar and then trim away the excess. To ensure a comfortable fit, simply slip two fingers underneath the collar, check the collar in this way regularly to ensure it continues to fit comfortably. This is particularly important if your pet is still growing. 

What does it kill? 

Seresto has been approved to kill fleas and ticks on dogs. The collar can also be used to treat lice and sarcoptic mange infestations and even prevent your pet from being bitten by sandflies that can transmit the disease Leishmaniosis.   

How does it work? 

Patented “Bayer Polymer Matrix” technology in Seresto collars releases the active ingredients (imidacloprid and flumethrin) in a controlled manner over 8 months. These are then distributed throughout your pet’s skin and fur. Ticks don’t even need to bite your pet, simply coming into contact with the product in their fur is enough to repel them. The two active ingredients are absorbed into a parasite’s body and they then bind to receptors in the nervous system interfering with the communication between nerves. This then leads to the bug becoming paralyzed and then dying. 

How long does it last?

Seresto collars have been proven effective for up to 8 months in most pets (depends a little on their lifestyle). Once you’ve opened the packaging, the collar starts to continually release the active ingredients, so it’s best to only open it when you’re ready to put the collar on your pet. 

There are certain conditions that can reduce the duration of this collar’s efficacy. While your pooch can be bathed monthly without removing the collar, too much shampooing or frequent swimming will reduce the amount of time the collar works. 

What Are the Active Ingredients in Seresto

  • Flumethrin: This ingredient targets lice and ticks and is a topical parasiticide.
  • Imidacloprid: This pesticide targets both larvae and adult fleas.  

How Are the Ingredients in Seresto Delivered? 

Using the “Bayer Polymer Matrix” technology, the ingredients are impregnated within the collar. These are then slowly released into your pooch’s skin and fur as the collar rubs against their body and spread through the lipid layer within the pet’s skin. Authentic Bayer Seresto collars are both odorless and non-greasy. 

How long does it take for Seresto to start working?

Fast-acting, the Seresto collar releases the active ingredients as soon as the packaging is opening and starts to spread through your pet’s coat once the collar has been applied. Fleas and their larvae are killed within 24 hours and while ticks may take up to 48 hours to be killed, one study has shown the collar to have some action against ticks within 6 hours of application (Stanneck et. al., 2012).

Safety, Risks, and Possible Side Effects 

While adverse effects can occur, these are thankfully rare with the Seresto collars. While the ingredients can cause sickness in pets and humans, the amounts required are far higher than those in the collar. If your pooch chews the collar, they may have a short-lived tummy upset including vomiting and diarrhea. Another question I’m often asked is what happens if the pupper becomes trapped on something by the Seresto collar. Luckily, these collars have a predetermined “breaking point” and for smaller pooches, a quick-release mechanism meaning the collar breaks to prevent injury to your pet. 

So, what are some of the signs to watch for once you pop the collar on your pet?

Itching: This usually lasts for just a few days after you apply the collar, and is more often seen in pets that don’t usually wear a restraint collar. Check that the collar isn’t too tight (can easily slip two fingers underneath) and monitor your pet for any other signs.

Hair loss: This is a very rare side effect and again usually only lasts for a short time without you needing to remove the collar. It’s usually due to the collar being a little too snug, causing hair loss due to friction. Ensure the collar is comfortably fitted and this should resolve quickly, though it can take a little longer for the hair to grow back. 

Dermatitis: Luckily, dermatitis or skin inflammation is exceptionally rare. If your pooch shows signs of persistent redness, itching, hair loss, pain, and wetness, or crusty skin then you should remove the collar and consult with your veterinarian. Topical medication is sometimes needed to resolve dermatitis, but most cases self-resolve once the collar has been removed. 

Redness: Another rare side effect of these collars, redness usually resolves within a few days and may be linked to the itching experienced by some pets in the first couple of days after application of the collar

Neurological signs: Incredibly rare, these signs include drooling, lethargy, and a ‘drunken’ walk. These are generally only seen in cases of an overdose such as a small dog having a large dog collar being applied without trimming the excess. Hence, the advice to trim away any excess strap once fitted to your pooch.

What we like about it

  1. Odorless and non-greasy
  2. Lasts up to 8 months
  3. Easy to apply
  4. Easily taken off if your pet experiences any adverse effects (very rare)

What we don’t like about it

  1. Expensive to purchase
  2. No prescription required (in the USA)
Our Rating:  4 out of 5! One word of caution when purchasing Seresto collars, ensure you are receiving an authentic collar as there are a number of counterfeit products on the market. Only purchase from a reputable retailer and check out our in-depth review on Seresto collars to find out what measures Bayer has introduced to allow you to rapidly determine if the collar you’ve purchased is authentic and thus safe for your pup. 

K9 Advantix II For Dogs

K9 Advantix II is a topical ectoparasiticide that you apply to your pooch once per month to protect them from pesky parasites. On the market since 2011, this product is also produced by Bayer.


Available in pre-measured, single-use pipettes, K9 Advantix II is easily applied to your pet’s skin. Part the hair between your dog’s shoulder blades and simply empty the contents of the pipette onto their skin. Don’t rub the product in and avoid touching your pet until the liquid has been fully absorbed and their fur has dried.

What does it kill?

Similar to Seresto, K9 Advantix II also targets fleas and ticks but this product also kills mosquitoes and biting flies. The mosquitoes killed by K9 Advantix II can transmit Dirofilaria immitis, also known as heartworm that causes Dirofilariasis/heartworm disease in pets and even humans on occasion.

How does it work?

The active ingredients (imidacloprid, permethrin, and pyriproxyfen) attacks the nervous system of pests, interfering with signaling between nerves. This causes paralysis and then death in these parasites.

How long does it last?

K9 Advantix II remains active within your pooch’s body for 4 weeks after application though some pets suffering from a severe flea infestation may need a repeat treatment within those 4 weeks. If you feel this may be necessary, you should speak with your veterinarian before applying any product (including K9 Advantix II) within the 4-week period to prevent adverse effects or overdose. K9 Advantix II can’t be applied for a second time within 7 days of the previous dose.

Remember once fleas start to feel the effects of the ingredients, they climb up the hairs on your pet’s fur so you may think the product hasn’t worked if you’re seeing more fleas after application but this isn’t so. Seeing fleas after you’ve applied the product is a sign it IS working!

What Are the Active Ingredients in K9 Advantix II?

  • Imidacloprid: This ingredient kills both adult and larval flea stages.
  • Pyriproxyfen: This ingredient is an insect growth regulator that stops flea larvae and eggs from developing to the next stage.
  • Permethrin: Targeting ticks and mosquitoes, permethrin also repels these bugs after application.

How Are the Ingredients in K9 Advantix II Delivered?

Each pipette contains a pre-measured dose suitable for your pet’s weight, this liquid is rapidly absorbed into your pooch’s skin after application. The ingredients are then stored within the oils in your pet’s skin where they persist for 4 weeks.

How long does it take for K9 Advantix II to start working?

Ticks that are attached to your pet at the time of application should be removed using an appropriate instrument as they are not killed immediately and could transmit disease. Ticks will be repelled within 3 days of an application while fleas on your pooch will be killed within 12 hours of application.

Safety, Risks, and Possible Side Effects of K9 Advantix II 

Side effects are a concern with all products but luckily with K9 Advantix II, these tend to be rare and mild. The most commonly reported adverse effects are mild itching or redness at the application site. Some paw-rents report puppies seeming a little tired after treatment too. 

As with Seresto, if your pet swallows some of the product they may experience short-term gastrointestinal distress such as vomiting or diarrhea. This product is toxic to cats so do NOT apply this product to your kitty, and once you’ve treated your pooch, keep your cat separate from them to prevent grooming where they may come into contact with the liquid. 

With all products, if your pet shows any signs of severe or persistent effects then you should take them to your veterinarian immediately. 

What we like about it

  1. Waterproof
  2. Suitable for young puppies just 8 weeks old
  3. Can prevent transmission of heartworm disease/Dirofilariasis through the product’s action against mosquitoes

What we don’t like about it

  1. Toxic to cats
  2. Heavily infested pets may need a repeat treatment

Our Rating:  4 out of 5! K9 Advantix II is a great topical product that is suitable to use on puppies as young as 8 weeks of age and may also protect pets against heartworm disease. While the product is reported to be waterproof and thus suitable for pets that love to swim, Bayer recommends bathing your pup just once per month to prevent interference with the medication from shampoo.

No product is 100% safe and any pet may suffer an adverse reaction, if you feel your pet may be sensitive to any product you should speak with your veterinarian before using. As always, if your pet has any adverse reaction to a medication you should contact your veterinarian immediately for advice.

Seresto Vs K9 Advantix II: What Are the Differences?

There are some obvious differences between Seresto and K9 Advantix II as Seresto is a collar application that lasts for up to 8 months while K9 Advantix II lasts just 4 weeks and is a topically applied liquid. There are some other differences too though.

Target Species: Seresto collars have been approved to kill fleas and ticks and have some action against lice and sarcoptic mange. K9 Advantix II also kills fleas and ticks, but can also prevent transmission of the heartworm, Dirofilaria immitis by killing mosquitoes. Seresto kills adult and larval fleas outright, as does K9 Advantix II, but the latter product also prevents the development of flea eggs and larvae to the next life stage.

Ingredients: One of the ingredients in K9 Advantix II, permethrin is toxic to cats so extra care needs to be taken if you have a kitty living in your home. The ingredients in Seresto collars are safe for cats though a dog collar shouldn’t be applied to your cat as overdose is possible.

Seresto and K9 Advantix II Similarities

On the surface, it doesn’t seem there are many similarities between Seresto collars and K9 Advantix II topical solution but there are some. 

Target species: Both products target fleas and ticks including flea larvae with similar onsets of action.

Ingredients: Imidacloprid is one of the products in both Seresto collars and the topical K9 Advantix II and this ingredient kills both adult and larval fleas. 

Seresto Vs K9 Advantix II: Effectiveness

Both of these products are effective at killing and repelling ticks. Seresto collars don’t target flea eggs though it does kill both larval and adult stages while K9 Advantix II does include action against flea eggs by preventing their development into larvae. One advantage K9 Advantix II may have against Seresto is its action against mosquitoes, while it doesn’t protect against heartworm directly, K9 Advantix II does reduce the risk of transmission by repelling mosquitoes. 

Seresto Vs K9 Advantix II:  Which Is Safer?

Safety-wise, both products are safe with rare side effects, and those that do occur tend to be mild and transient. If your pet has a reaction to Seresto you can simply remove the collar if necessary, while it’s not that simple to remove K9 Advantix II from your pet as bathing will only remove product that hasn’t absorbed so effects can be seen for up to 4 weeks. If your pet lives with a cat you do need to take extra precautions when treating your pooch with K9 Advantix II. If your pet suffers any reaction to either product you should contact your veterinarian immediately. 

Ease of Use

Both Seresto and K9 Advantix II are super easy to use for the majority of pet parents. Your pet will simply feel like they’re having their collar applied when you are using the Seresto product, though you need to be careful trimming the excess, as you don’t want to cut your pupper. K9 Advantix II can be spilled if your pet is very wriggly and you need to part their hair to apply it directly to the skin so this can be a two-person task with some pets. 

Which Scores Better on Price?

K9 Advantix II is available in packets of 2 or six pipettes. The price of this product will vary depending on the size of your pet and which packet you purchase. A pack of 6 pipettes for a small dog weighing between 11-20lbs will cost about $78 equating to around $13 per month. 

Seresto collars are an expensive up-front cost at approximately $70 for a dog under 18lbs. Since the collar lasts for up to 8 months the monthly cost is just $7 for most pets which would be almost half the monthly price of K9 Advantix II.

Does My Dog Really Need Flea & Tick Medication?

I get asked this question quite a lot and I can’t stress this enough – YES! All pets need flea and tick preventative treatments no matter where they live. These bugs aren’t just irritating to pets, some dogs are actually allergic to flea bites and can suffer extreme reactions to just a single bite so continual prevention is essential for these pets. 

Another concern is the nasty diseases that these bugs can spread to your pet (and some of these diseases affect us, humans, too). Many of these are difficult to treat and may not be curable which can lead to very expensive vet visits and may even shorten your pet’s life so preventative medications are essential. 


My puppy is only 10 weeks old. Can I still use Seresto or K9 Advantix II? Both of these products are safe to use on your puppy as it’s suitable to use on puppies just 8 weeks of age. You may choose to use K9 Advantix II as your puppy will grow rapidly and may grow out of their Seresto collar before the 8 months but you do need to trim at least some of the excess to prevent overdose (though this is very rare), this is very important if your puppy is very small.

My Dog is pregnant or is nursing young puppies. Can I still use one of these medications? You should always speak with your veterinarian before using any product on your pregnant or nursing bitch. These products should be used with caution in these animals as their safety hasn’t been fully assessed in clinical trials. 

Can I Combine Flea Treatments? No! Never combine flea treatments! If you feel a product isn’t working for your pet (remember seeing more fleas is actually a sign the product is working) then you should discuss this with your veterinarian for advice. 

Are these Products Child Safe? Seresto is safe for a person to come into contact with it, though you should always ensure your child washes their hands after coming into contact with your pet or the collar and prevent young children from licking or chewing on the collar as this can cause tummy upsets.

K9 Advantix II can also cause tummy upsets if ingested but it can also cause some redness or irritation to their skin or mouth (if a toddler puts their fingers in their mouth after coming into contact with the product) so I always advise my clients apply this product at bedtime when children won’t come into contact with the product while it dries on their pet. 

Seresto Vs K9 Advantix II Final Thoughts

Seresto Vs K9 Advantix II Final Thoughts

Choosing a flea and tick preventative for your pooch can be difficult but some things to bear in mind when selecting one is the bugs the product targets, how long is the product effective, is it easy to use, how expensive is the product, and are there any safety concerns of the product.

Both of these products kill fleas and ticks that are the primary targets of your quest, both products target other bugs so if you live in an area where there is a high incidence of heartworm disease then you should consider using K9 Advantix II to try to reduce transmission of the parasite though you will still have to use a dedicated heartworm medication.

If your fur-baby is a water-pup that loves to swim every chance you can still choose to use Seresto but you need to be aware that the duration of efficacy will be reduced and may only protect against fleas for up to 5 months. You may elect to use K9 Advantix II in this case, but if your pet needs regular shampooing, you won’t receive any additional benefit over the Seresto collar. 

We hope this Seresto vs K9 Advantix II review has helped inform you better about both of these products and aid in your decision-making process. Which product you choose will depend on your pet’s lifestyle and your requirements so if you’re unsure or haven’t used either product before then you should discuss this with your veterinarian before purchasing and remember to always purchase from a reputable source to ensure you’re applying a safe and authentic product to your pooch.

Stanneck, D., E.M. Kruedewagen, J.J. Fourie, I.G. Horak, W. Davis & K.J. Krieger (2012). Efficacy of an imidacloprid/flumethrin collar against fleas, ticks, mites, and lice on dogs. Parasit. Vectors. 20(5).

Photo of author
Since graduating from Dublin, Ireland in 2013 with an honors Veterinary Medicine degree, Edele has enjoyed working with as many species of animal as possible. Edele is currently working in clinical practice while studying towards Advanced Practitioner status with the RCVS in the UK. Passionate about education and writing, Edele’s goal is to maximize the pet-owner bond and welfare through education accessible to everyone. Never found without her middle-aged Weimaraner, Purdy (who still thinks she’s 18 months old), Edele spends her limited time outdoors with her horses, hiking and traveling home to Ireland to spend time with family.

1 thought on “Seresto Vs K9 Advantix II: What The Woof Is the Difference?”

  1. Thank you for this article. Ticks have been SOOOO bad this year. I found 13 crawling on ME on a 10 minute walking with my fur baby to the stream. And several on her as well of course.
    I’ve always used K9 Advantix ii, but a friend just told me about Seresto so I just ordered one from, but now I see that it was coming from a 3rd party company I’d never even heard of and has ZERO reviews. This made me very skeptical, so I just cancelled my order and paid a little more from Amazon.
    And Zoe LOVES to be in the water, so I’ll also need to consider that it won’t be good for the whole 8 months. I’m gonna anticipate about 4 months and will re-evaluate in a few.
    Thank you for the information and the authenticity warning!!!


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