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How Safe is My Pet’s Flea Preventative?

May 29, 2009 By: Dr. K Category: Questions

flea1If you have a pet, you’ve most likely heard about the Environmental Protection Agency’s recent investigation into the safety of topical flea and tick preventatives. As a whole, prescription spot-on flea and tick preventatives are fairly safe. As with any medication, allergic reactions and drug sensitivities can occur. Most sensitivities involve irritation at the site of application or several days of lethargy following application. Other signs can include but aren’t limited to poor appetite, seizures, and rarely death. These side effects are uncommon when using medications as directed in healthy animals. The adverse event rate to these medication reported by the EPA is still very low compared to average event reaction rates in human medicine.  Over 100 million doses of spot on flea preventatives were sold in the United States last year. Around 44,000 adverse events were reported to the EPA. That is a rate of 0.04%, an increase from 0.02% in 2007.  Some adverse events will always go unreported. A very generous estimate of a total of 1,000,000 adverse events would yield a rate of 1.0%. This is still quite low compared to the adverse event rate of medications given to hospitalized human patients. Their average adverse event rate is 6.7%.

One of the things the EPA has failed to note during their investigation is the emergence of multiple new spot-on treatments in the last year. Promeris and Profender are both new topical medications advertised for the treatment of fleas and/or intestinal parasites, respectively. Both of these products emerged on the market last year and could account for the substantial increase in reported adverse effects. In addition, with recent pet food recalls, consumers may be more likely to monitor for and report any adverse side effects. Media sensationalism only heightens the public’s awareness of potential side effects and may also ignite a flurry of reported incidents.

Frontline and Advantage have been around for years and the “adverse reaction” rate has held relatively steady. When used as directed in healthy animals of the appropriate age, these products have long been considered safe by veterinarians. Most veterinarians do not recommend over-the-counter flea and tick preventatives due to the lack of scientific based evidence the active ingredients work and lack of regulation.

In addition, despite many warnings and attempts at client communication people are STILL using canine only products on cats. Cats are exquisitely sensitive to permethrins and pyrethrins along with amitraz. Use of these products on cats can result in their deaths. Over-the-counter (OTC) products are typically very poorly marked as to canine only, feline only dosing which leads to errors in use. Be cautious with whatever flea and tick preventative you use.


More is not better. Cats are not small dogs.

5 Comments to “How Safe is My Pet’s Flea Preventative?”


  1. How do you feel about the oral preventatives, such as Comfortis?

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  2. I have never used Comfortis so I cannot speak firsthand on its efficacy. Based on the research and minimal adverse effects reported, I believe this product is reasonably safe for dogs and works quickly to kill fleas. The most common adverse event reported in a study of nearly 400 dogs was vomiting.

    This oral flea preventative is similar to other products that have been on the market for ages. Luferon is the flea insecticide in Sentinel and Program. Nitenpyram is the active ingredient in Capstar. All of these products have proven safe over the years as well.

    The bigger issue in veterinary medicine is owner compliance. Pet owners are more likely to regularly use one or two products versus three products for complete parasite protection. I always recommend heartworm preventatives as well as a flea AND tick preventatives. Practicing on the east coast, tick infestations are severe. Ticks transmit Lyme Disease, Rocky Mountain Spotted Fever, Anaplasma, and Erhlichia. If a product eliminates fleas only, owners are required to purchase a tick collar as well as a heartworm preventative. Expense goes up, compliance goes down, and the pet is at risk for developing disease. I am more inclined to recommend products that cover both fleas and ticks, like Frontline and Advantix (in dog only households) or products that cover both fleas and heartworms, like Revolution and Advantage multi.

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  3. Thanks. I was concerned about if Comfortis covered ticks, but I guess not. Being that we live in Florida I should probably discuss this with our vet. She is still scratching, but I believe this may be caused by mosquitoes or allergies.

    Thank you for the insight. My dog did experience vomiting; however, I have found that if I feed her it reduces the chance of vomiting.

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  4. I think your math is off here. The “generous estimate” you mention is 1 million. The total was 100+ million. 1 in 100 is 1% (by the very definition of percentages). You can also phrase it as 0.01–but use either 0.01 OR 1%.

    To get a percentage, divide incidents by total possibles and then multiply by 100%. For example:

    (44,000/100,000,000) x 100% = 0.044%

    Still a very small number.

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  5. G: Calculation error noted and corrected! Thanks!

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