Frontline Spot On (active ingredient fipronil) is advertised as a treatment for cat fleas:

Kills fleas within 24 hours

Kills fleas for up to 5 weeks in cats

My mum recently went to her vet to buy some, but was told they don't sell it because it doesn't work. The Wikipedia article for fipronil claims that:

flea populations appear to be developing a genetic resistance to its effects

Is fipronil an effective treatment for cat fleas?

  • Just a few fleas can cause great discomfort to your cat, especially if she is one of the many animals allergic to fleabites. So, normal treatment techniques may be only partly effective. Dec 30, 2012 at 12:26

1 Answer 1


While partial fipronil resistance in feline fleas has been reported, this resistance does not appear to be widespread, according to this study which found fipronil to be effective against feline fleas (this study used dogs as subjects, though I don't think that should make much difference as feline fleas were one of the parasites that was investigated).

This review suggests that most reports of resistance are the result of improper use and misunderstanding of flea biology and life cycle.

However, given the potential for resistance, they recommend an integrated approach to flea control, using both medication (including the use of both adulticides and insect growth regulators (some products such as Frontline Plus (which contains fipronil and (S)-methoprene) combine these in one treatment) in multiple-pet households) and treatment of the environment (vacuuming, insecticides, etc.).

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