Categories: flea treatments

Fipronil in Frontline Spot On flea treatment only 48% effective

Frontline Spot On flea treatment is perhaps best known of all Flea treatments in America and in the UK. It is certainly well known and widely used. The active ingredient is fipronil, a broad-spectrum insecticide which disrupts the insect’s central nervous system. It causes hyperexcitation of the nerves and muscles.

A study published on 5 October this year tells us that 62% of cats treated with fipronil were “still found to be carrying fleas despite treatment”. With respect to dogs, 44% were found to have fleas despite treatment with fipronil. The study contrasted the efficacy of fipronil as an anti-flea treatment with that of fluralaner (a systemic insecticide administered orally). The researchers found that 4.1% cats and 1.4% dogs treated with fluralaner still had fleas after treatment. Fluralaner was found to be the most effective flea treatment in cats and dogs. It is a relatively new treatment. The chemical is an ingredient in the product Bravecto®.

Fipronil effectiveness. Image: PoC. Words from the study referred to in this article.



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The question I immediately had was whether fluralaner is safe. Fipronil has a track record and to the best of my knowledge is considered relatively safe. I say “relatively” because all insecticides given to cats and dogs are unsafe. Cat and dog owners make them safe by using them with great care through following the instructions. Personally I don’t use them because I don’t trust them.

Fluralaner appears to be reasonably safe although it can cause side effects. It is ingested rather than dropped onto the skin of the animal. That probably makes it less safe in any event but I don’t know. There is a study on the internet about fluralaner. It is called “Suspected neurological toxicity after oral application of fluralaner (Bravecto®) in a Kooikerhondje dog. They report that the drug is generally well tolerated in dogs but can cause neurological dysfunction in individual dogs. Personally, I don’t like to read that sort of stuff. I don’t know how it might affect domestic cats negatively i.e. the side effects in cats. It probably has a similar potential danger to cats. I will leave it to individual cat guardians to make their own decisions, of course.

The point of this short article is to publicise the study which tells us that fipronil, an ingredient of the most widely used cat flea treatment, does not seem to be that effective with almost 2/3 of cats still having fleas after being treated with the chemical. Once again you make your own mind about that.

There is a need for people to understand the prevalence of cat fleas and how to eliminate them. There’s also a need for people to research the efficacy of The treatments and to understand their potential dangers. These are insecticides, nasty chemical poisons. Great care is needed to use them properly. I’ve said it before but there are too many cat deaths because their owners carelessly used dog flea treatments on their cats. It is a horrible way to kill your cat.

Dog flea treatment packaging needs to be changed to protect cats

Veterinarians should provide good advice about the best flea treatments. I don’t know whether we can completely trust veterinarians to do this because they probably have affiliations with wholesalers and manufacturers which obliges them to support certain treatments over others. The products they support might not be the most efficient. It is up to cat guardians to dig around a bit and be on their toes to pick the best treatment if they want to use one.

As an aside, the study about the relative ineffectiveness of fipronil also found that, in the UK, cats and dogs in central Wales and the Welsh borders, were more than twice as likely to have fleas than anywhere else in the UK! Dogs from North Wales, the North Wales borders, south Wales and south-west England were between three and 4.5 times more likely to have fleas than elsewhere in the UK. That’s another rather interesting piece of cat and dog trivia. It indicates that people living in Wales and the Welsh borders are less careful about their cats and dogs having fleas than in other parts of the UK. What does that tell us about the attitude of Welsh cat and dog owners?

Michael Broad

Hi, I'm a 71-year-old retired solicitor (attorney in the US). Before qualifying I worked in many jobs including professional photography. I have a girlfriend, Michelle. I love nature, cats and all animals. I am concerned about their welfare.

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