Frontline for Cats: Dosage, Safety & Side Effects

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cat receiving a flea treatment

Frontline is a brand of topical, “spot-on” flea/tick treatment and prevention containing the ingredient fipronil. The patent on fipronil expired in 2010, leading to the release of many generic products. Frontline has since become only available as the products Frontline Plus and more recently, Frontline GOLD.

Frontline for Cats Overview

Medication Type:
Phenylpyrazole antiparasitic
Topical liquid solution
Prescription Required?:
FDA Approved?:
This topical medication is approved by the EPA for cats.
Life Stage:
Cats 8 weeks of age and older
Brand Names:
Frontline Top Spot for Cats and Kittens, Frontline Plus for Cats and Kittens, Frontline Gold for Cats; there are many generic OTC brands for fipronil. Generic brands for Frontline Plus include PetArmor Plus for Cats and EctoADvance Plus for Cats.
Common Names:
Fipronil (Frontline Top Spot), Fipronil + (s)-Methoprene (Frontline Plus, Fipronil + (s)-Methoprene + Pyriproxyfen (Frontline Gold)
Available Dosages:
A single dose size is available for cats and kittens weighing 1.5lb or more

In this article, you’ll learn about the different Frontline products available for cats, the ingredients they contain, what types of parasitic pests they target, possible side effects to consider, and some frequently asked questions.

About Frontline for Cats

Fipronil is the primary active ingredient in all Frontline products for both dogs and cats. As per its indication, it kills fleas, kills ticks, and targets chewing lice. It can also kill mosquitoes. While not labeled for it, it has also been successful in treating for chiggers and the sarcoptic mange mite that causes scabies.

Fipronil is a phenylpyrazole antiparasitic agent, and is technically classified as a pesticide. In invertebrates (including insects like fleas and arachnids like ticks and mites), it interrupts GABA-regulated nerve channels, causing neurologic overexcitement, disruption and death.

Frontline “spot-on” products are applied to the surface of a small target area or “spot” of the skin, usually at the back of the head or neck.

Fipronil collects in the oils of the skin and hair, allowing for continual release, lending to its 30 day period of efficacy. Per the product label, it takes about 24 hours to spread throughout surface oils on skin and hair to provide complete protection.

It is important to note that while these pesky pests are affected by Frontline by coming in contact with the skin and don’t have to actually bite a kitty to die, Frontline products do not provide true repellency that would prevent fleas or ticks from coming in contact with a pet.

What Does Frontline Do for Cats?

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Frontline products are among the only topical “spot-on” options for cats providing protection against both fleas and ticks. Other products for cats may only protect against fleas and some ticks, or just fleas.

While the original Frontline could only kill adult fleas and did not treat all life stages of the flea, Frontline Plus includes the addition of (S)-methoprene, which is an insect growth regulator that additionally targets flea eggs and flea larvae, helping to interrupt the life cycle and prevent new adults from hatching and developing.

Frontline GOLD additionally includes another insect growth regulator called pyriproxyfen that is more efficient at targeting flea eggs and larvae, eliminating fleas faster than its predecessor.

Side Effects of Frontline for Cats

When used properly, side effects to Frontline products are uncommon. Frontline products are only labeled for cats older than 8 weeks of age. Topical products like Frontline should never be ingested.

The most commonly reported effect is a temporary irritation at the application site. More red, irritated skin has been reported, but is considered rare. If this occurs, it is more likely a kitty has a hypersensitivity or allergy to one of the ingredients.

All three ingredients currently found in Frontline products (fipronil, (S)-methoprene, pyriproxyfen) generally appear to have a low potential for toxicity both topically and even if accidentally ingested.

However, the products are very bitter tasting. If a kitty were to lick recently applied Frontline off either themselves or a housemate, the bitter taste alone can lead to excessive drooling, agitation, and sometimes even vomiting.

According to DVM360’s article “Toxicology Brief: The 10 most common toxicoses in cats” this effect is typically not a true toxicity, but a sometimes dramatic reaction to the bitter taste. Providing milk or liquid from a tuna can help resolve the signs in short order.

To avoid this from happening, it is important to apply any topical flea/tick product to the skin in front of the shoulder blades at the back of the neck, a location even the most flexible cat cannot reach to lick. In multiple cat households where lots of co-grooming occurs, separating housemate kitties for up to 24 hours after application to allow the product to fully dry may be advisable.

Although Frontline products for dogs and cats contain the same active ingredients, there are slight differences in the percentages of active ingredients and inactive ingredients, so the dog products should never be shared with cats.

Using Caution With Other Flea/Tick Products

cat scratching itself

Some dog flea/tick products that used to be used in cats contain permethrin, which is extremely toxic to cats. Luckily, these products are now required to include a warning against use in cats.

While Frontline for Cats has been established as a safe product, the active ingredients may be found in other products in combination with other ingredients that are not safe for cats. This is especially the case with dog products like K9 Advtantix II that contains permethrin, which is extremely toxic to cats.

Fortunately, these products are now required to include a warning against use in cats. But just to be safe, when selecting a flea/tick product for your kitty, always make sure the product includes a picture of a cat and indicates the product is specifically for cats.

It is also always advisable if you have a pup and kitty who like to hang out together or groom each other, to separate them for 24 hours after applying a topical product to your dog, especially if the product contains permethrin.

If you have any concerns for potential toxicity, even if you think your kitty might have just licked some Frontline off her fur and is having a bitter taste reaction, it is always best to contact your veterinarian, or the ASPCA Animal Poison Control Center for further advice.

And lastly, topical products like Frontline have been known to cause skin and eye irritation in people. It is best to avoid contact with the solution during application and to wash your hands after.

Frontline for Cats Dosage

Frontline products are typically applied every 30 days for the best protection. Protection against ticks is limited to 30 days requiring a monthly application, though protection against fleas can be reportedly for up to 6 weeks according to the manufacturer.

Always follow all instructions on the packaging for any topical product you use for your kitty. Frontline vials come with a perforated applicator tip that needs to be broken off or snipped off with scissors. It is then best applied by parting the fur and applying the entire contents of the vial to a cat’s skin along the back of the neck in front of the shoulders where a kitty cannot reach to lick it off of himself.

While Frontline products are considered to be waterproof, make sure not to bathe your kitty for 24-48 hours after an application. Bathing shortly before application may also reduce its effectiveness.

If for some reason you are unsure if the product was administered correctly or whether all of it was applied, it is usually safest to not apply an additional dose.

If you have any questions about application or safety for Frontline products or any topical product, make sure to get in touch with your veterinarian.


Frontline products have been around for over 20 years, and are considered by veterinarians to be generally safe to use as long as the feline only product is administered. The active ingredients are still largely considered to be effective against fleas and ticks as well.

Topical products like Frontline can all have different combinations of ingredients targeting different parasites that can sometimes be confusing. Make sure to clarify any questions you have about the best product for your kitty by having a chat with your vet.

Drug Dosing Disclaimer: We are only able to provide doses for medications that are FDA approved for use in cats and only as the label guidelines dictate. For medications that are used off-label we can only provide guidelines and safety information for use. Safe and appropriate dosing for off-label medications can only be determined by a primary care veterinarian.

We encourage you to work with your veterinarian to determine if a particular medication is appropriate for your cat. Changing or adjusting a dose for your cat on your own without consulting with a veterinarian can carry risk. We do not encourage use of medications prescribed for human use in pets without first consulting with a primary care veterinarian.

Frequently Asked Questions

How effective is Frontline for cats?

Frontline products are still considered to be effective against fleas and ticks. The newer Frontline GOLD is also more efficient at killing fleas by more quickly targeting eggs and larvae. 

However, the question of flea or tick resistance to these products and the idea that they don’t work comes up often. The 2017 article “Perception vs. Reality: Insecticide Resistance in Fleas” from DVM360 that refers to an article published in American Veterinarian that same year addresses this topic. 

An entomology (“bug science”) professor from the University of California heavily investigated this question and concluded that while resistance has been seen to some flea treatment or prevention products, true chemical resistance in fleas with fipronil, imidacloprid, and some other newer products on the market has not yet been demonstrated.

In many cases, when a pup or kitty parent is still seeing live fleas on their pet after a product has been applied, this issue can most often be traced back to incorrect use or application of the product, as well as poor expectations. Following are some common errors or misperceptions.

  • Incorrect application. (i.e. applied to the fur not the skin, failing to apply the whole volume of product, failure to properly puncture or open a vial prior to application).
  • Failure to apply to all pets in the household. If one pet brings fleas indoors, they can jump onto all pets in the home. If all pets are not treated at the same time, flea infestations can persist.
  • Bathing. Baths are a common go-to, especially when live fleas are seen. However, while waterproof, Frontline products need 24 hours to spread throughout the oils on the skin. Bathing shortly before or after application removes oils from the skin as well as possibly the product itself. 
  • Not Treating Long-Enough. It can sometimes take as long as 3 months to clear out a flea infestation. So while most veterinarians advise year-round protection against fleas and ticks, a product like Frontline should be used every month for at least 3 months during an active infestation. Flea eggs not cleared from the home environment are likely to continue hatching every couple of weeks, meaning a kitty that received only one monthly dose of Frontline can get infested again a few weeks later if the dose is not repeated the next month.
  • Not Treating Year-Round. Fleas have been known to over-winter indoors. Treating pets for only certain months of the year can leave open gaps in prevention for infestations to occur.
  • Failing to Treat the Environment. Because one flea can lay up to 50 eggs in just one day, the amount of eggs in a home environment with fleas can be staggering. If the environment is not treated effectively, continually hatching fleas may continue to be found on a treated pet. 
  • Perceiving Products as Repellents. Always remember that most topical products like Frontline do not have repellency action, meaning that fleas and ticks must come in contact with the skin to be killed. Heavily-infested outdoor areas as well as poorly-treated indoor infestations can be sources for large numbers of adult fleas to “suddenly” appear on a treated pet. 
  • Frontline Makes Fleas Hyper. Frontline’s action against the neurologic pathways of fleas causes them to become hyper excited before dying. This means you may actually view more of them initially after application as they jump to the surface of a kitty’s furry coat.

If You Still Think There’s a True Product Issue

If you feel you have applied a product properly and are addressing a flea infestation according to your vet’s instructions and still feel that a product is not working well, make sure to bring those concerns to your vet or contact the manufacturer of the product. 

How quickly does Frontline work for cats?

According to the manufacturer, Frontline can start to kill fleas within 4 hours and can kill 100% of fleas on a pet within 12-18 hours. It is important to remember however that when first applied, it can take up to 24 hours for Frontline to be fully effective. 

Frontline GOLD works a bit faster, with the ability to start killing fleas within 30 minutes.

When it comes to ticks, it can take up to 48 hours for them to be killed. According to the product label, mosquitoes are killed within 24 hours for up to 14 days and within 48 hours for up to 28 days.

What is the difference between Frontline and Frontline Plus for Cats?

The original Frontline product contained only fipronil, which kills only adult fleas and ticks. Frontline Plus contains the additional insect growth regulator (S)-methoprene, which targets fleas eggs and larvae. Frontline GOLD has a second insect growth regulator that reduces the time it takes to start killing fleas. 

Around the year 2000, Frontline Plus was released and the original Frontline started to be phased out. Frontline GOLD was released just a couple of years ago. Currently only Frontline Plus and Frontline GOLD are available. 

Which is better for cats: Frontline or Advantage?

Advantage products available for cats include Advantage II and Advantage Multi and they have some differences from Frontline products. Advantage contains imidacloprid, which like fipronil also targets the nervous system of the flea. However, instead of causing excitatory neurologic behavior before death, imidacloprid causes more of a neurologic paralysis. Because of this difference, some pet parents may perceive Advantage II as being more effective, though in the end, both products are doing the same thing.

Advantage II also has pyriproxyfen just like Frontline GOLD, which targets flea eggs and larvae. According to the manufacturer, Advantage II can kill all fleas within 12 hours of application. This may be more fast-acting than Frontline Plus but probably similar to Frontline GOLD.

Both Frontline products and Advantage II only require contact with the skin for fleas and ticks to die. Both are also considered waterproof within about 24-48 hours of application.

The biggest difference between Frontline and Advantage II is that the latter is only effective against fleas. It has no protection against ticks or lice. While ticks are less commonly found on cats compared to dogs (possibly because cats are far more fastidious groomers) they still present a risk for disease, especially for outdoor cats that may wander through heavily tick-infested areas. This would be the main consideration when choosing between the two products. 

Advantage Multi contains imidacloprid plus the ingredient moxidectin. Moxidectin adds a spectrum targeting ear mites, the intestinal parasites hookworms and roundworms, and mosquito-borne heartworms. Advantage Multi does not contain pyriproxyfen, so its flea spectrum is limited to adult fleas.

Heartworm is a tough subject in cats. Testing for heartworms is not as routine in cats as it is in dogs since testing in cats can only detect heartworm in about 50% of cases. However, more recent data has shown that more cats may be affected by heartworm disease than previously thought. 

Some cats may clear a heartworm infection on their own, while others may die suddenly and without warning. Because there is also no safe and effective treatment for cats with heartworm, using a product that can prevent heartworm infections in cats may be advisable, especially for outdoor cats and cats living in regions endemic for heartworm. This would be the main advantage, if you will, to choosing Advantage Multi over Advantage II or Frontline products.

Because Advantage Multi is a heartworm preventative, it is not available over the counter like all of the other products discussed in this article, and must be obtained through a prescription from your vet.

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About Dr. Chris Vanderhoof, DVM, MPH

Dr. Chris Vanderhoof is a 2013 graduate of the Virginia-Maryland College of Veterinary Medicine (VMCVM) at Virginia Tech, where he also earned a Masters in Public Health. He completed a rotating internship with Red Bank Veterinary Hospital in New Jersey and now works as a general practitioner in the Washington D.C. area. Dr. Vanderhoof is also a copywriter specializing in the animal health field and founder of Paramount Animal Health Writing Solutions, which can be found at Dr. Vanderhoof lives in the Northern Virginia area with his family, including 3 cats.

9 thoughts on “Frontline for Cats: Dosage, Safety & Side Effects”

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  1. Mags Deakin

    having successfully used frontline flea treaent for cats for years, my latest application was nearly one week ago and i am still finding the odd flea whilst grooming my cat. should i reapply before the reccomended one month interval

    thank you for all the help and advise yu offer
    kind regards

    Mags. Rosie’s Mum ‘

    1. Avatar photoDr. Chris Vanderhoof, DVM, MPH Post author

      Hi Mags, thanks for your question. Compared to failure of the product, it is more common if you’re still seeing the occasional flea, that there may be eggs or pupae in the home environment that are periodically hatching and finding their way to your kitty. It’s always important to remember that Frontline (and most topical products) is not a repellent, so any fleas in the environment must come in contact with your cat’s skin to be killed by the product. This can continue to happen for a few weeks until all of the growth stages of the flea are spent. Extra vacuuming, steam cleaning, and possibly having an exterminator come to treat the home, may be needed to more fully rectify the environmental component.

      I would only consider reapplying if there’s a possibility the product may have been applied incorrectly or if your kitty had a bath shortly before or after application, etc. In the Frontline article, in the FAQ section, the first question “How Effective is Frontline for Cats” lists several reasons why folks may still see fleas after applying a topical product.

      Now, if you feel that none of these other causes are likely, and you are certain the home environment is decontaminated, you could talk to your vet about another product to use in its place. Resistance to Frontline and other topical products is possible and has been documented, but is considered extremely rare compared to the several other reasons to still see fleas.

  2. Dawn

    My cat became weak in her back legs on two occasions using advantage II. First time it happened we thought she had managed to ingest some from grooming, so we put a collar on the next time but the same happened. She would loose the power in her back legs at times, suddenly and wouldn’t be able to move, then have to lie down. This went on for about two weeks each time. Her sister had none of these side affects. At the moment we have put a flea collar on them but it doesn’t seem to be doing much good, so are thinking about trying frontline but worried as the same might happen but worse than the advantage. Any help and advice welcomed.

    1. small mallory photoMallory Crusta

      Hey Dawn, thank you for sharing; that sounds very concerning. Frontline Plus and Advantage II feature different insecticides, so I wouldn’t be sure that the two would cause the same side effects, but without talking with a vet and confirming exactly what triggered this reaction, it makes sense that you would be hesitant to try just about anything. I’d think about taking her off of the preventive altogether, switching to a basic oral medication for the time being, and talking with your vet to determine what will be the best and safest route for her.

    2. Joey

      I don’t know if you still read the comments posted in reply to your question but…..ask yourself…..would YOU put these chemicals on your children or yourself? Probably not huh? A chemical of ANY TYPE IS A CHEMICAL! Poison! Do your animals a solid, go with NATURAL PRODUCTS! Not this garbage big pharma pushes! They’re all just alike! All about the money. Save your beloved animals! If YOU won’t use it for yourself, don’t use on THEM either! That goes from the garbage in the nasty foods they peddle! RESEARCH! Never totally rely on the so called “expert’s”. Most are not anyway and REFUSE TO LISTEN to the PROOF that natural products and foods WORK!

    3. Avatar photoDr. Chris Vanderhoof, DVM, MPH Post author

      Hi Joey,
      Thanks for your comment. All opinions, as long as they are respectful, are welcome. I of course, have a different perspective from your own. Prior to Frontline and many of our other products that have since come to market, flea and tick control in pets was extremely difficult. I remember seeing swollen ticks literally dropping off of dogs in the boarding kennel I worked in. We regularly had to give dogs flea dips which were tedious. We simply don’t see that kind of thing so commonly anymore and now I think the level of concern for the diseases these things carry has been switched out for concern over side effects and toxicity, which overall is uncommon. Some people may find natural remedies that work for them and their pets. But I’ll never forget the owner who insisted on using tea tree oil on his dog for scabies and fleas, which continued to get worse for months before he relented to use Revolution and both the fleas and scabies resolved in a couple weeks. The crystal therapy didn’t work either. These products are not just a big pharma money grab. They do work. Natural products are not better, but simply another option that carry their own risks. I had a client once that used peppermint oil on her cat for fleas, the cat licked it off and got very sick from it to her surprise. You even have to be careful using diatomaceous earth. Nothing is without risk. But I’d rather use deep woods off on myself to avoid getting a tick borne illness than lemongrass oil.

  3. Ted

    I have 3 doses of frontline that are markedFrontline plus-1, 34ml H64305 07 2015.on the applicator! I’m not sure if these were for my dog or my cat. I don’t have the box they came in. I don’t want to put this on my cat if it is meant for my dog. Can anyone identify which this was made for? Thanks!

  4. L. Wind

    Hi I want to mention my vet was very insistent on using the drops on my new to me cat. She was itchy there and developed a wound! The next time I mentioned it and said we didn’t want it because of that. They reapplied it and the same thing happened. We then called and it didn’t happen after I was very insistent. But I keep reading this is not, in fact, rare at all.

    1. Avatar photoDr. Chris Vanderhoof, DVM, MPH Post author

      Hi L,

      Thank you for sharing your experience. Skin reactions like this are the most common side effect of any topical medication. Cats may make mild skin irritations worse by scratching at the site and causing more trauma or a skin infection in the area. This would be considered different from a more severe skin reaction that occurs on its own, which is usually a hypersensitivity or allergy.

      If skin irritation is seen, washing the site with warm soapy water to remove as much residue as possible may help lessen the irritation before a kitty digs or scratches at it too much. Of the millions of cats likely on Frontline or similar products, such more severe reactions are still rare.

      It’s easy to get the opposite impression when doing searches for Frontline side effects, as you’re likely to find posts consisting of folks reporting side effect concerns and it may seem more common than they truly are. All the same, if a clear reaction occurs, that product should be avoided in the future. It’s possible another topical product may not cause the same concerns, unless a kitty has very sensitive skin or a skin allergy condition.