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Pets and Pesticides: Let’s Be Careful Out There
Are Over-the-Counter Flea-and-Tick Treatments Really Safe for Dogs and Cats?
By M.B. Pell and Jillian Olsen | December 16, 2008
http://www.publicintegrity.org/investigations/pesticides/articles/entry/1080/

Last June Diane Bromenschenkel applied a flea-and-tick product to her English 
pointer, Wings, so the dog wouldn’t get ticks while hunting pheasant in the 
tall grasslands of western Idaho. Wings, a healthy five-year-old with a sleek 
white coat and a chocolate brown mask, enjoyed long walks in the woods, bacon 
treats, and burying things in the yard. But three months after the pesticide 
was applied, the animal was dead.

It was just hours following the use of the product that Bromenschenkel knew 
something was wrong. She noticed her dog walking around in a daze. Wings was 
unresponsive. On the advice of her veterinarian, Bromenschenkel tried to wash 
off the treatment —Bio Spot Spot On Flea and Tick Control for Dogs — but the 
next day Wings was still suffering.

The dog stopped eating and drinking despite the application of appetite 
increasers, said Patricia Pence, the veterinarian and owner of South Wind 
Veterinary Hospital in Nampa, Idaho, where Wings was treated. “The anorexia 
is a direct result of the Bio Spot,” Pence said. She believes the insecticide 
in Bio Spot damaged the portion of Wings’ brain responsible for hunger and 
thirst. So she inserted a feeding tube into the dog’s neck and for the next 
three months Bromenschenkel and Wings were in and out of the veterinary 
hospital.

During this period, Bromenschenkel woke up every two hours at night to give 
Wings an injection of liquid nutrient through the neck. She spent thousands 
of dollars on vet bills. Despite the best efforts of Bromenschenkel and 
Pence, however, the damage was done. In September, Wings’ kidneys failed and 
Bromenschenkel made the difficult decision to put her dog to sleep. In days 
Wings had gone from a healthy dog, running alongside horses in the Owyhee 
Mountains, to an emaciated wreck, chasing phantom birds in the kitchen. 
“What’s so terrible about it is that if you had known, you would never have 
used it,” said Bromenschenkel of the Bio Spot.

Bio Spot contains a 45 percent solution of the active ingredient permethrin, 
a synthetic neurotoxin belonging to the pyrethroid family of chemicals. Bio 
Spot is one of several over-the-counter spot on (meaning squeezed on to a 
particular spot) anti-flea-and-tick products that consumers apply to cats and 
dogs between the shoulder blades and sometimes at the base of the tail. The 
animal’s natural oils spread the insecticide over its body, making its skin 
and fur inhospitable to parasites. These pyrethroid-based flea and tick 
treatments — from Hartz, Sergeant’s, Farnam, and Bayer — are approved for 
sale by the Environmental Protection Agency (EPA), and they are readily 
available at grocery stores, specialty pet retailers, and hardware stores. 
But they are also linked to thousands of reported pet poisonings, and they 
have stirred the ire of pet owners, the concern of veterinarians, and the 
attention of regulatory agencies.

Manufacturers and distributors of over-the-counter spot on treatments say the 
products are generally safe and effective when used properly, but they 
concede there are cats and dogs that either have a preexisting condition or 
an acute sensitivity to these treatments that leads to an illness.

The industry position, however, may dismiss safety concerns too casually. At 
least 1,600 pet deaths related to spot on treatments with pyrethroids were 
reported to the EPA over the last five years, according to an analysis of EPA 
pesticide incident exposure data by the Center for Public Integrity. That is 
about double the number of reported fatalities tied to similar treatments 
without pyrethroids, such as Frontline and Advantage — although these 
products also have critics.

Pyrethroid spot ons also account for more than half of “major” pesticide pet 
reactions reported to EPA over the last five years — that is, those incidents 
involving serious medical reactions such as brain damage, heart attacks, and 
violent seizures. In contrast, non-pyrethroid spot on treatments accounted 
for only about 6 percent of all major incidents.

In the last five years, the EPA received a total of more than 25,000 reports 
of pet pesticide reactions of every sort — fatal, major, moderate, and minor 
— to over-the-counter pyrethroid spot on products. This compares to 10,500 
reports of all pet incidents related to shampoos, powders, sprays, collars, 
dips, mousses, lotions, and towels. This analysis does not take into account 
how much of each product was used over the last five years as the EPA does 
not have that information.

The EPA cautions that it does not confirm the authenticity of these reports 
and most of the claims come from consumers and not trained toxicologists. The 
EPA uses the database to observe broad trends and to identify significant 
spikes in incidents for specific products and chemicals.
Warning Signs

A few websites, run by pet owners, specialize in educating people on the 
dangers of over-the-counter spot on treatments. Almost every day someone 
posts a new horror story, often involving a late-night emergency trip to the 
vet. “I cannot stop crying knowing that if I hadn’t put that on them then 
they would still be here playing and loving as they always did before,” reads 
one post about a woman’s loss of two kittens in October.

The concentrations of pyrethroids in over-the-counter spot on pet treatments 
range from a 40 percent to an 85 percent solution, eight to 17 times stronger 
than the strongest pyrethroid product currently approved for use on humans. 
Neither the EPA, which generally regulates topically applied products, nor 
the Food and Drug Administration, which generally regulates orally applied 
pet products, has a product registered for human application containing a 
pyrethroid concentration above 5 percent, and that FDA-approved product 
requires a doctor’s prescription. In fact, the Sergeant’s Gold Squeeze-On for 
Dogs warning reads: “Harmful if swallowed or absorbed through skin,” while 
the application portion of the label directs people to apply the treatment 
“to the dog’s skin.”

But these high concentrations may be necessary in pet products because pets 
are more apt to come in contact with fleas and ticks, according to Margaret 
Rice, chief of the EPA’s Office of Pesticide Programs registration branch. 
Some human products, like the 5 percent permethrin shampoo, also call for 
more of the product to be applied than the just under one ounce in the spot 
on treatments.

Pyrethroid toxicity targets nerve and muscle cells in pets, according to a 
study published in The Veterinary Journal in June 2008. The study found that 
dermal exposure by application to the skin or coat is the most common route 
of toxic exposure, potentially causing hyperexcitability, tremors, profuse 
salivation, and seizures. The seizures can result in brain damage or, less 
frequently, death.

Representatives of Central LifeSciences, the parent company of Farnam, the 
distributor of Bio Spot, said that they could not discuss the death of Wings 
because their investigation of the incident is still underway. The company 
said reports of adverse reactions are rare, about three of every 10,000 doses 
for cat products and five of every 10,000 doses for dog products. These 
numbers include incidents that resulted from misapplication and preexisting 
medical conditions, according to Central LifeSciences. “Bio Spot Spot On Flea 
& Tick Control for Dogs has met all applicable EPA registration requirements 
and is approved for topical use on dogs,” the company said in a letter they 
sent in July to one unhappy customer whose dog had recently died.

Hartz Mountain Corp. representatives said via e-mail that the active 
ingredient in the company’s spot on dog treatments, the pyrethroid 
d-phenothrin, and the active ingredient in their cat product that kills adult 
fleas, the pyrethroid etofenprox, are categorized as least toxic by the EPA, 
as opposed to the active ingredient in Frontline, fipronil, and the active 
ingredient in Advantage, imidacloprid, which, while much less concentrated, 
are rated as moderately toxic. Sergeant’s cat spot on treatments also contain 
etofenprox, but the company has spot on dog products that contain 
cyphenothrin and products that contain permethrin, moderately toxic 
pyrethroids.

Another possible explanation for the number of incidents is that consumers 
often misuse flea and tick products, causing the sickness that pet owners 
later blame on the treatments, said Jennifer Windrum, a spokeswoman for 
Sergeant’s. “Pet owners feel incredibly guilty if they misapply it to their 
pet,” Windrum said. “It’s easier to blame a company.” Common misapplications 
include applying more powerful dog products to cats, applying the product 
where the pet can lick it, and using a treatment meant for a large animal on 
a small one. The directions on these products include a description of where 
to apply, sometimes a diagram, and if it’s a dog product, multiple warnings 
not to it use on cats.

Forest Desmond and his wife Marilynn received a letter from Sergeant’s 
offering to pay their $125 vet bill after they applied Sergeant’s Gold 
Squeeze-On for Dogs to their five dogs. The letter from Sergeant’s also 
stated that the company believed the dogs may have licked the product off 
each other, a violation of the application instructions. “The Sergeant’s Gold 
Squeeze-On for Dogs is for external use only and has several warnings on the 
package indicating such,” the letter says. The product’s label does not 
instruct consumers to keep dogs separated after treatment, but Sergeant’s has 
submitted a request to the EPA to have the label changed. Sergeant’s “Look at 
the Label” website already recommends people separate their pets after 
application.

“What they’re trying to say is the dogs licked it off each other and thereby 
took it in internally, but they didn’t lick it off, it burned their skin,” 
Marilynn Desmond said. “My response to that is they’re trying to shift the 
blame from the producer to the user. If this had been my first dog, I might 
have fallen for that.”

The authors of the study in The Veterinary Journal agree that misuse of 
pyrethroid products is often the cause of illnesses, although they also point 
out that accidental ingestion by mouth or during grooming is another common 
exposure route. “The best way to avoid serious problems is by educating pet 
owners to use products strictly according to label directions,” the study 
says. “Veterinarians must advise clients using flea care products to read and 
follow label instructions completely before applying them on or around their 
pets.” The rub here, some veterinarians say, is pyrethroid spot on treatments 
are over-the-counter products, easily purchased without consulting a 
veterinarian.

Michael Murphy, a veterinarian and toxicologist at the University of 
Minnesota, speaking for the American Veterinary Medical Association, said he 
rarely hears of pet reactions to spot on treatments, and when he does it’s 
usually because a consumer applied a stronger dog product to a cat. But for 
some pet advocates, the misapplication explanation misses the point. The 
Humane Society of the United States has heard this reasoning before, but 
still recommends pet owners avoid over-the-counter spot on products and only 
use treatments recommended by veterinarians, according to Stephanie Shain, 
the organization’s director of outreach. “With the number of complaints we 
get it seems like an extraordinarily high rate of problems,” she said. “Even 
if it is owner error much of the time, something is not working the way it 
should be. I think at the very least there need to be much stronger warnings 
on those products cautioning pet owners about the dangers involved with using 
them.”

Others express similar concerns. “Sometimes I wonder why it’s still 
approved,” said Mark Grossman, a co-owner and veterinarian of Roanoke Island 
Animal Clinic and a toxicology consultant for the Veterinary Information 
Network. “They can’t get it out there without the EPA approving it. 
Apparently they say if they do enough tests, it’s still OK. In real life 
though, I think we’re seeing more problems than we should.”


Paying the Bills

After Samantha Ribble’s English bulldog, Bella, and pug, Chloe, developed 
oozing sores where she placed drops of Sergeant’s Gold Squeeze on for Dogs, 
she asked Sergeant’s to pay her veterinarian bill, $309. Without admitting 
any liability, Sergeant’s agreed to pay the bill, on the condition that 
Ribble sign a release that read as follows: “I agree not to make any oral or 
written communication which disparages or has the effect of damaging the 
reputation of or otherwise working in any way to the detriment of Sergeant’s. 
This Release shall inure the benefit of Sergeant’s heirs, legal 
representatives, successors, and assigns and shall bind me and my heirs, 
legal representatives, successors, and assigns.” In the same letter, 
Sergeant’s notes that its products are closely regulated by the EPA and 
tested in “accordance with EPA rules and regulations in order to ensure that 
the products are safe.”

This is true. The EPA approved the company’s pyrethroid spot on treatments 
just as it has approved all spot on treatments, but the agency has a history 
of approving pet products in the past only to pull them from the market 
later. The EPA approved the use of chlorpyrifos products, cancelled for use 
on pets in 2001; diazinon products, cancelled for use on pets in 2001; and 
phosmet products, cancelled for use on pets by 2004. The products were 
approved, defended aggressively by the chemical industry, and then yanked off 
the market. They were largely replaced by pyrethroid products, which are 
generally thought to be less acutely toxic.

Even pyrethroid pet products, however, have been approved and then pulled. In 
2000, the EPA received a rash of reports from cat owners concerning Hartz 
Mountain Corp.’s Advanced Care Once a Month Flea & Tick Drops for Cats, a 
spot on treatment containing the pyrethroid d-phenothrin. The agency received 
reports of cats losing their hair, salivating uncontrollably, experiencing 
tremors, and sometimes dying. Judy Van Wyk of Rhode Island filed a lawsuit 
against Hartz in November 2001 on behalf of pet owners whose cats had reacted 
to Hartz cat drops. The complaint alleged that “Hartz has also known since at 
least March 2001 that adverse reactions in cats to the Drops is a common 
problem.” The suit was voluntarily withdrawn in November 2002, which may 
indicate an out-of-court settlement, but neither Hartz nor Van Wyk would 
comment on the case.

Three years later, after the company and the agency experimented 
unsuccessfully with stronger warning labels, the EPA entered into 
negotiations with Hartz Mountain Corp. and the company agreed to stop selling 
the product.

Rice, chief of the EPA’s Office of Pesticides registration branch, said the 
agency knows it has had problems with these products in the past. Still the 
EPA holds the position, as with all products registered by the agency, that 
pyrethroid-based spot on treatments are not harmful if consumers follow label 
instructions. The 25,000 reported incidents alone will not change this 
conclusion, Rice said. The EPA is investigating pyrethroid incidents, 
involving both humans and pets, and when it finishes this process — the EPA 
does not have a target date yet for doing so — it may make regulatory 
changes, but until then the agency stands by its conclusion. “Our decisions 
to register these products and compounds are done with significant data,” 
said Marion Johnson, branch chief of the EPA’s Office of Pesticide Programs 
registration division. “When we register these products, we feel they’re 
safe.”

So safe in fact that Johnson said the EPA does not expect any pets will have 
a sensitivity to spot on products leading to an illness; the incident 
reports, in Johnson’s view, are not at all definitive. Manufacturers, for 
their part, do acknowledge the existence of sensitive cats and dogs. “There 
is a certain percentage of dogs out there that, just like with humans, will 
have an allergic reaction no matter what,” Windrum, the Sergeant’s 
spokeswoman, said. Less than 1 percent of sales result in an adverse reaction 
when the product is used as directed by the label, she said.

The EPA cannot make its own assessment because unlike the regulations 
directing the FDA’s approval of human products, the Federal Insecticide, 
Fungicide, and Rodenticide Act does not require pet products to undergo field 
trials prior to approval. So the agency can only require less extensive 
testing, often only on one breed of dog or cat. This makes it difficult to 
predict the effects on the broader population of users.

The EPA also considers the need consumers have to control fleas and ticks on 
their pets and the benefit provided by low-cost pyrethroid spot ons when 
making decisions about these products. The over-the-counter pyrethroid spot 
ons are typically half the price of Frontline and Advantage.

EPA scientists continue to monitor the safety of pet pyrethroids. In 
November, several EPA employees at the Office of Research and Development 
authored a piece in BMC Genomics, an online journal that publishes 
peer-reviewed articles, that found exposure to the pyrethroids permethrin and 
deltamethrin in young rats “could result in detrimental effects on 
neurological function later in life.” The study found this was a possibility 
even using doses of permethrin that do not cause immediate, acute symptoms. 
The authors of the article suggested many other avenues of research — 
including examining the effects of other pyrethroids on neurological function.

The EPA also hopes to improve the quality of incident reports through an 
online reporting system for veterinarians that began this fall. In addition, 
the agency is analyzing pet incidents to identify patterns that may lead to 
additional labeling or further regulatory action, and reviewing the process 
of approving pet products to see if changes are warranted.

“We need to make sound scientific decisions,” Johnson said. “On the one hand 
we have the data that says this product might be safe and on the other we 
have incidents that say it might not be.”