Warning that the powerful poisons can endanger dogs and cats, the U.S. Environmental Protection Agency will require new instructions and labeling for on-spot flea products.

The products, including the popular Frontline and Advantage brands, are small vials of liquid pesticides that pet owners apply monthly to the backs of dogs or cats to kill fleas and ticks. The EPA began investigating the products after discovering a sharp rise in the number of pets reported to be sick after they were treated.

The yearlong investigation, conducted by a team of veterinarians assembled by the federal agency, concluded that certain pets – small dogs between 10 and 20 pounds – are most susceptible to the problems, which include rashes, vomiting, diarrhea and seizures.

EPA Assistant Administrator Steve Owens said Wednesday that no products are being banned at this point, but “we’re going to be watching the situation very closely.”

New instructions and warnings are expected on product labels within the next several months. If these steps don’t reduce the problems, “we will take more significant action. We will remove products from the market if we have to,” Owens said.

Fleas and ticks can cause discomfort and diseases for many dogs and cats around the country. As a result, the on-spot treatments are commonly recommended by veterinarians.

Many pet owners who use the treatments think they are applying medication to their pet, but they actually are treating them with potent pesticides, including permethrin, which also is used to kill pests on crops and yards.

“These are poisons that we are applying to our pets,” said Owens, who said it is a personal as well as a professional issue for him because he owns two dogs and three cats. “Pet owners should exercise caution.”

Incidents reported by consumers who used the products on their pets rose from 28,895 in 2007 to 44,263 in 2008, an increase of 53 percent in one year.

Most of the problems were minor, such as skin rashes, but about 600 dogs and cats died in the incidents reported in 2008, EPA records show.

Chihuahuas, shih tzus, miniature poodles, Pomeranians and dachshunds had the most reported incidents, according to the EPA report released Wednesday. For products containing cyphenothrin, those breeds accounted for 33 percent of the reported problems. For products containing permethrin, shih tzus, bichon frise, chihuahuas, yorkshire terriers and maltese were involved in more than 25 percent of the incidents. K-9 Advantix for Dogs contains permethrin and some Sergeant's products and Sentry's Pro XFC contain cyphenothrin.

“Small breed dogs were more commonly affected with the number of incidents out of proportion to their popularity,” the EPA report says.

The problem might be the dose. The agency is telling manufacturers to narrow the range of weights identified for their products.

“We will make clear that certain products cannot be used on smaller animals,” Owens said.

In addition, the investigation found that cats were sickened when products intended for dogs were used on them. Permethrin is particularly dangerous for cats and is not used in any on-spot treatments for cats.

EPA officials said they will meet with each manufacturer individually to go over the changes that the agency wants, such as more precise instructions regarding the proper dosage for pets’ various weights. Also, markings should distinguish better between cat products and dog products, and similar brand names will not be allowed for both. New labels also would advise people to keep cats away from treated dogs for a period of time.

Manufacturers seem willing to work with the EPA, so the changes are expected this year, Owens said. "They realize this is a serious problem that they need to address," he said.

Merial, Ltd., a Georgia-based company that makes Frontline flea and tick treatments, said in a statement that it “will work cooperatively with the EPA to help pet owners to use our products safely.”

The company, however, said the incidents were rare and minor. “The number of adverse events reported for Frontline has remained consistently low since the product's introduction in 1996,” the statement said.

Owens said the EPA’s investigation found incidents “all across the board,” with all brands and products.

EPA officials said they cannot explain the sudden jump in reported problems, except that it may be due to increased use of the on-spot treatments or more awareness among pet owners.

The investigators could not verify that all the illnesses among the pets were actually linked to the products. “The incidents have not been verified and may have causes other than exposure to the pesticide,” the report says.

In some cases, pet owners were misusing the products, but EPA officials stressed that most of the blame goes to the industry, not consumers, because of the poor labeling.

“When used appropriately in most cases they are safe,” Owens said, but “the labels are unclear right now.”

Owens said the actions announced Wednesday “are really just the first step.” The EPA also plans to require more rigorous testing of products, similar to the Food and Drug Administration’s requirements for animal medications. “We are not getting the kind of data we need” to predict whether pets will have problems with these products, he said.

In addition, new on-spot products will be granted only conditional and time-limited approval so that side-effects can be investigated before the products are fully approved. Manufacturers also will have to disclose more information about the inert ingredients – the non-pesticides – in their products, and some of those ingredients will be restricted.

This article originally ran at Environmental Health News, a news source published by Environmental Health Sciences, a nonprofit media company.