Flea resistance to frontline

Updated June 19, 2018

Frontline is a top-recommended flea and tick protection product for cats and dogs, according to the Frontline website. Frontline contains fipronil, which kills adult fleas in 18 to 48 hours. Frontline also contains methoprene, which kills flea eggs and larvae.

Losing Effectiveness

In 2007, Fox News in Florida reported that Frontline might be losing its effectiveness. Fleas may be becoming immune to it. Dr. Bill Kroll, a Florida veterinarian told Fox News that fleas are resistant to fipronil in particular. Kroll estimates that 75 per cent of his clients who use Frontline say that it isn't working.

Only Certain Fleas

It is possible that only certain fleas develop a resistance to fipronil, says Dr. Byron Blagburn, a specialist in fleas at Auburn University. Blagburn says not enough fleas are resistant to Frontline to make a major impact.


If you use Frontline on your dog or cat and still see fleas, the reason may not be that Frontline is ineffective. You may have noticed the fleas before they are going to die, says Dr. Susan Ralston, a veterinarian who works for Frontline. Another reason may be that you are not using Frontline correctly. If you use Frontline on your dog or cat and fleas persist after several days, you should try a different product, according to Fox News.

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About the Author

Laura Agadoni has been writing professionally since 1983. Her feature stories on area businesses, human interest and health and fitness appear in her local newspaper. She has also written and edited for a grassroots outreach effort and has been published in "Clean Eating" magazine and in "Dimensions" magazine, a CUNA Mutual publication. Agadoni has a Bachelor of Arts in communications from California State University-Fullerton.