Changes coming to common rodent poison

Potent anticoagulants to be discontinued

October 16, 2014 (published)
By Edie Lau

VIN News Service photo
Trays of rat- and mice-killing pellets remain on the market, but not for long. Under pressure by the U.S. Environmental Protection Agency, the maker of d-CON is reformulating products and changing packaging of rodenticides sold for household use to reduce the chances of accidental poisonings of children, pets and wildlife.
The small paperboard boxes of aquamarine pellets long deployed by households battling infestations of mice or rats soon will go off the market in a push to protect wildlife, children and pets from accidental poisonings.

Reckitt Benckiser Inc., maker of d-CON brand of rodenticides, agreed this year to a directive from the U.S. Environmental Protection Agency to discontinue 12 products that don’t meet the agency’s updated safety standards.

The standards prohibit the residential use of powerful toxicants known as second-generation anticoagulants, which are designed to kill rodent pests with a single feeding. Also prohibited for consumer use are pellets and other forms of bait that can’t be secured in bait stations.

Under its agreement with the EPA, Reckitt Benckiser will stop producing the problematic products by the end of the year, and stop distributing them to retailers by March 15, 2015. Retailers are allowed to sell the products until their supplies are depleted.

The change has been brewing for years. The EPA began scrutinizing the risks of accidental-poisoning by rodenticides in 1999, initially driven by reports of children being exposed to the toxicants, and later, concerns about the effect on wildlife. The danger for children is eating the baits directly; for wildlife, it’s eating poisoned rodents.

Eventually, worries about pet safety arose, as well. Rodenticide ingestion is among the top 10 causes of calls to the Animal Poison Control Center operated by the American Society for the Prevention of Cruelty to Animals. In 2013, the center received 6,803 reports of accidental poisoning by rodenticides, equal to 18.6 per day, according to Dr. Tina Wismer, the center director.

The EPA acted in 2008 to ban second-generation anticoagulants from household use, a move that Reckitt Benckiser initially resisted. Except for traps that don’t deploy rodent-killer, the company’s d-CON line relies entirely on anticoagulants, ingredient information on its website shows. Second-generation anticoagulants appear in all formulations but one.

The company plans a national rollout of replacement products next year but has declined to specify what active ingredient or ingredients those products will contain.

It’s a critical piece of information for doctors, including veterinarians, treating victims of accidental poisoning. Up to now, the predominant poison used against rats and mice has been anticoagulants, compounds for which an antidote exists. Other types of rodent poisons are more difficult to treat.

In explaining its objections to the EPA action, Reckitt Benckiser indicates on the d-CON website that it was concerned about shifting to a neurotoxin for which there is no known antidote. Why the company ended its fight against the new rodenticide standard is unclear, but Reckitt Benckiser suggests that it will continue using anticoagulants in its new product line:

“While other manufacturers have chosen to shift to active ingredients that include a powerful neurotoxin, new d-CON bait stations will continue to utilize effective ingredients for which an antidote (Vitamin K) is readily available.”

Among d-CON chemical rodenticides for which the company gives ingredient information, one contains a first-generation anticoagulant, diphacinone, which is still allowed for household use.

The problem with first-generation anticoagulants is that mice and rats have developed resistance to their effects. These compounds include warfarin, a drug used in medicine to prevent clots from forming or growing. At toxic doses, the drugs cause death by internal bleeding.

The rodent resistance problem brought about the development of a second generation of anticoagulants that are more powerful, able to kill in a single feeding. They also linger longer in the body. Their potency and persistence heighten the danger for wildlife that feed on rodents, including predators such as eagles and scavengers.
The newer and older anticoagulants alike work by inhibiting an enzyme involved in the function of vitamin K, which is integral to the body’s manufacture of blood-clotting proteins. Vitamin K is the antidote to anticoagulant poisoning. Depending on how long ago the poison was ingested, treatment also may involve inducing vomiting and administering activated charcoal to stop the body from absorbing the toxicant. Some cases may require transfusions of whole blood and plasma, as well.

According to the Safe Rodent Control Resource Center, first-generation anticoagulants are “excreted fairly rapidly by mammals, usually within a week.” By comparison, second-generation anticoagulants are not easily excreted but persist in organs such as the liver and elsewhere in the body.

The second-generation anticoagulants prohibited by the new EPA standards are brodifacoum, bromadiolone, difethialone and difenacoum. The prohibition applies only to household use; the poisons may continue to be used in agriculture and by commercial pest control operators.
Although the new limits are meant to better safeguard pets as well as wildlife, the shift may be a mixed blessing for companion animals. That’s because other rodenticide makers are turning to bromethalin, a nervous-system poison for which no antidote exists.

“If you have an animal that’s been exposed to bromethalin, if it’s just happened, we can give activated charcoal, and that can stop the signs from occurring,” Wismer said, “but if the animal has brain swelling and it’s seizuring, mortality is almost 100 percent.”

For that reason, veterinarians are “not happy, because we used to be able to treat them … and now we’ve got animals that can die,” she said.

Broadly, the move away from the most potent anticoagulants “makes sense,” said Wismer, who also serves as a consultant at the Veterinary Information Network, an online community for the profession. “ … But looking at what we do for a living, it’s going to make our lives more difficult.”

She added wryly, “Sometimes it’s not all about us!”

Among poisonings by rodenticide, 65 percent of calls last year involved anticoagulants, figures at the Animal Poison Control Center show. About 25 percent involved bromethalin, which has been available since 1985. “It already has a pretty decent market share,” Wismer observed.
When ingested, bromethalin attacks the brain, causing swelling in the myelin sheath, a layer of protein and fatty substances that insulate the nerves. However, it is less persistent in the body than second-generation anticoagulants, and doesn’t concentrate in muscle tissue.

Also, in the case of dogs, the lethal dose of bromethalin is relatively large — some 36 times that of second-generation anticoagulants, Wismer said. Birds, too, appear to be somewhat resistant to its effects.

Cats are a different matter. Wismer said cats, like mice and rats, are very sensitive to bromethalin.

Cats and dogs also differ in how they come to be poisoned. Cats are more apt to eat poisoned rodents, whereas dogs are more likely to sniff out and eat the bait itself, possibly including the packaging. “We’ve had dogs move refrigerators or get under the stove” to get at bait, Wismer said.

Requiring more secure bait stations, along the lines of enclosed plastic boxes with blocks of bait that rodents can’t carry out, is meant to make it harder for children and pets to access the rodent-killer. But tamper-resistant boxes aren’t foolproof. Dr. Charlotte Means, another VIN toxicology consultant, noted, “Dogs like to play, and the bait can smell good — the right dog can crack open a bait station, no problem.”

The important thing, Means and Wismer say, is that consumers know what’s in the products they’re using. Baits with different active ingredients may be hard to distinguish from one another by appearance. Up to now, Means said, an educated guess that a mystery rodenticide was an anticoagulant usually was correct. Soon, that may not be the case.

Beyond anticoagulants and bromethalin are a couple of other possible active ingredients. Some brands use cholecalciferol, a form of vitamin D that causes kidney failure by overdosing the body on calcium. It doesn’t have a large market share, judging from calls to the Animal Poison Control Center. Said Wismer: “It (accounted for) less than 1 percent of phone calls last year, which is good, because it’s very difficult to treat; very expensive.”

Another chemical used as a rodenticide is zinc phosphide, which reacts with water and acid in the stomach to form highly toxic phosphine gas.

Means advises consumers using rodenticides to keep a written record of the products deployed in their household. “People need to know what the dog actually ate,” she said. “We can tell you what to do a whole lot better if you can tell us that… And if you have a pest control company, make sure you get a receipt with the name of the product. Ask exactly where they’re putting things; how many blocks you have out there.”

Means said she’s hopeful that the changes in rodenticide packaging and ingredients will call the public’s attention to the possible risks of using the products. “I think overall it is a positive thing,” she said. “It might make people think more. As consumers are educated, hopefully, they will be more careful about where baits are placed, and accidents might be avoided.”

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