Frontline Reactions in Cats

Fleas and ticks, hit the bricks; go somewhere else to get your kicks.
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Just the thought of fleas or ticks biting or sucking Kitty's blood makes you cringe. Fortunately, topical monthly flea and tick preventives such as Frontline make such parasites a thing of the past. While reactions to Frontline are relatively rare in cats, they are not unheard of.


Frontline contains fipronil, while Frontline Plus contains fipronil and s-methoprene. Fipronil kills both fleas and ticks on Kitty's body, while s-methoprene does in the flea eggs and larvae. You simply apply the product to the skin between Kitty's shoulder blades, where he can't reach to lick it. Kitty's body is usually flea and tick-free within 12 hours of the initial application. Fipronil stays in the oil glands on the cat's skin and is generally effective for the next 30 days before reapplication is necessary.

Side Effects

Most reported side effects are mild. The majority concern reactions at the application site, with the cat's skin losing hair there or becoming red and irritated. When applying the pesticide, make sure it doesn't get into Kitty's eyes, where it can cause vision damage. Since it can also damage your eyes, wear gloves when applying the product. If either one of you gets Frontline in your eyes, wash the eyes with cool, fresh water and call the vet or the doctor at once.

Always make sure you are giving Kitty the correct dosage. While Frontline comes in topical dosages specifically for cats and different sizes of dogs, there's also a spray version. Always read the label and follow the directions carefully. Overdosing with Frontline might cause side effects such as vomiting or excessive salivation. If you have other pets in the household, keep an eye on them to make sure they don't lick the area between Kitty's shoulder blades, where Frontline is applied.


Some cats are allergic to Frontline and Frontline Plus. If Kitty develops hives or a rash after application, or if any sort of swelling is present, call your vet immediately. In a worst-case scenario, an allergic cat can go into anaphylactic shock and die if not treated at once.


Don't use Frontline along with other pesticides. Kittens under 8 weeks of age shouldn't receive Frontline at all, nor should pregnant cats or nursing mothers. If Kitty is very old or has a compromised immune system, discuss with your vet whether Frontline is safe to use. If Kitty takes prescription medications or over-the-counter supplements, check with your vet to make sure they're compatible with Frontline.

Always check with your veterinarian before changing your pet’s diet, medication, or physical activity routines. This information is not a substitute for a vet’s opinion.

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