How Does Frontline Work on Cats?

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As a cat owner, you want to be on top of your cat's health and well-being. An important part of their care is keeping them safe from fleas, ticks, and other parasites. One popular flea and tick preventative for cats is called Frontline. We have compiled this guide to provide you with a complete breakdown of what Frontline is and how it works for your cat.

Frontline is a spot-on or topical treatment containing an insecticide called Fipronil. The liquid mixture is absorbed through your cat's skin, killing attached fleas, ticks, and chewing lice while preventing future infestations within a one month period. 

All cats are subjected to the risk of flea and tick infestations, even if they live only indoors. Every feline owner should be familiar with preventatives used to protect our furry friends. Read on as we talk about Frontline's ins and outs and what options you have if Frontline is not the best choice for your companion.

A cute fluffy white and gray cat scratching his chin due to tick and lice infection, How Does Frontline Work on Cats?

When should Frontline be applied?

You can apply Frontline on your cat once they reach eight weeks old and are over 1.5 pounds in weight. Waiting until your furry friend reaches these requirements is essential to avoid any toxicity that can be caused by the insecticide found in Frontline.

Amazon offers Frontline for cats and kittens in an 8-dose pack, here.

This flea and tick preventative is given monthly. With the initial application, these ectoparasites on your cat will die and fall off. Unfortunately, fleas or flea eggs can live in the environment much longer. Using Frontline on a monthly basis will stop the flea life cycle within your home and provide your cat with constant protection.

Watch this short video that showcases how to apply Frontline to your cat.

Is It Safe To Use Frontline Twice A Month?

Frontline will remain in the system for a full 30 days. It is not completely safe to apply this preventative twice a month, and it is not necessary. Never exceed the stated dose on your Frontline package.

Applying Frontline twice a month is unlikely to cause an overdose for your cat, potentially creating skin reactions or damage at the application site. Your cat may experience skin irritation, sensitivity, and redness. To keep your cat comfy, it is best to stick to the recommended once a month dose.

A veterinarian putting flea drops on a cat

What Happens If You Use Too Much Frontline?

Applying too much Frontline can create toxicity or poisoning in your cat. This product comes in measured pipettes with specific instructions to apply only one pipette to the skin at the application time.  If you apply an additional pipette or apply a Frontline product not specifically made for cats (or for your cat's weight), you risk putting their health in danger.

The active ingredient in Frontline is an insecticide called Fipronil. This insecticide works by inhibiting the neurotransmitters of the central nervous system. When this inhibitor reaches exposed parasites, it overexcites their nervous system and kills them quickly. When your cat is dosed appropriately, there is enough insecticide to kill off parasites without affecting your cat's central nervous system. However, if Frontline is given in excess, your cat can experience Fipronil poisoning.

What Does Fipronil Poisoning Look Like?

If your cat gets exposed to too much Frontline, the symptoms can be concerning and sometimes even fatal. The primary symptoms of Fipronil poisoning include uncoordinated movements, abnormal gait, hyperreactivity, tremors, muscle cramps, convulsions, and seizures.  These symptoms are directly related to the central nervous system enduring toxicity.

Your cat may experience more general symptoms like lack of appetite, agitation, vomiting, twitching, and weakness. The severity of the symptoms will depend on the dose of Frontline given and the kind of exposure (skin, inhalation, ingestion, or eyes).

These symptoms will typically appear a few hours after the medication is applied. If you know your cat was dosed inappropriately, you should wash off any Frontline left on the skin and visit your veterinarian for aftercare and supportive measures.

A cat owner taking her cat to the vet for frontline treatment

How does Frontline spread?

Frontline is applied to the skin between your cat's shoulder blades. This is the recommended application site because it lowers the risk of your cat grooming the area where the medication lies. You want Frontline to be absorbed through the skin, not ingested.

When this preventative is applied topically, it will seep into the skin's sebaceous glands and slowly release throughout the body. This slow-release allows for long-term protection against ectoparasites such as fleas and ticks.

Fipronil is lipophilic, meaning it loves to attach to fat cells. The sebaceous glands absorb and spread about 5% of the Frontline, and the rest is found in fatty tissue. This process of medication absorption through the glands is called translocation.

How Long Does It Take For Frontline To Start Working?

If you notice your kitty has a flea or tick infestation, you are probably antsy to get this sorted. Once Frontline is applied to your cat, it takes up to 24 hours for the preventative to spread over the entire body.

A cat scratching on his back

All fleas and lice on the body of your cat will die within 18 hours of contact. In some cases, you will see fleas falling off your cat after just four hours. For ticks, it will take 48 hours or about two days for all to die and fall off your cat. Your cat should be completely clear of ectoparasites by two days after the initial application of Frontline.

A cat receiving flea treatment from the vet

Frontline continues to protect your cat for a 30 day period and helps maintain a flea-less environment in your home. The insecticide, Fipronil, is the ingredient that cures your cat of any infestations they experience. The other main ingredient in Frontline is S-Methoprene. S-Methoprene is responsible for stopping flea eggs from hatching.  This is why a monthly application of Frontline is important.

How Do You Know If Frontline Is Working?

When your cat is experiencing a flea or tick infestation, you will notice them scratching often and seeming generally uncomfortable. A quick part to the hair can reveal obvious flea dirt. You've applied Frontline and have waited a 24 hour period.  You know that Frontline is working when you see fleas or ticks starting to fall off your cat's body.

A cat scratching its back on a room

If the infestation is not severe, these parasites may not be as obvious when dying and falling off.  If your cat has stopped scratching, flea rashes start to clear up, or your cat feels more comfortable, these are indications that this preventative is doing the trick for your companion.

What To Do If Frontline Isn't Working?

You may have concerns about Frontline not working for your cat. You've applied the medication, but your cat is still itching, and fleas are present when you comb through their hair. What should you do?

It is best to find the reason why Frontline is not working for your cat.  Some possible issues include the following:

  • The source of the infestation has not been treated.
  • Frontline has not been applied appropriately.
  • Not enough time has passed.

If you feel like Frontline is not working on your cat, the best place to start is ensuring your environment is free of fleas or other mites. This can include vacuuming regularly, using insecticide sprays, or bringing in an exterminator. Infestations of fleas cannot be cured overnight, unfortunately. Practice patience and give the treatments some time to work.

One of our members posted an issue they were having with Frontline -kunoichi9280 reported, "I tried Frontline on my 15-week old kitten a couple of weeks ago. It worked great for a week, and then it just stopped. I'm doing all the other flea treatment things recommended, and it's having zero impact (of course, I have a sucky bagless vacuum that probably isn't doing great on the carpets)".

This is a case of the environment not being treated completely. You can keep treating your cat, but without the appropriate measures taken in the home, the fleas will find their way back into your cat's fur.

Maybe you find yourself at a dead-end with Frontline. Do not worry! There are an array of antiparasitics available for your cat. Outside Frontline, other options available include Bravecto, Advantage, Revolution, and more. Always talk with a professional in the veterinary field if Frontline is not the best choice for your companion.

Read more on our blog post, "Cat Fleas" here.


Frontline is a very popular flea and tick preventative that is applied monthly for your cat. It primarily works through cellular absorption after being applied to the skin of your cat. There is a risk of over-dosing, and in some cases, Frontline does not work for an individual. It is always best to consult your veterinarian before starting a new preventative to ensure you have picked the right one for your furry friend.

Looking for more information on flea treatment? Have a look at our blog post, "How To Treat Fleas in Young Kittens."

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