Visiting Vet: Rodenticides

Keep your pet safe when targeting vermin.


It happens all the time. You see a mouse scurry across the kitchen, or a rat run under the birdfeeder in the yard. You go to Shirley’s and buy “rat poison,” or call an exterminator who puts product in your basement or garage. Then you forget all about it. But Snoopy, the schnauzer, doesn’t forget. One day you leave the basement door open. Snoopy retrieves the bait. You find him happily gnawing rat poison in the living room. “Bad dog! Drop it!” you shout, pulling the remains from his mouth. Then, if you are smarter than your dog, you call your veterinarian immediately.

The conversation usually goes something like this: “OMG! Snoopy just ate rat poison! Can I come right down?” “Well, first we need to know exactly what kind of poison and how much he ate.” “It’s rat poison! It’s that green [red, yellow] block! Can I come right down?” “Many different kinds of poison come in green [red, yellow] blocks. Do you have the package it came in?” “No, but I’m pretty sure it’s d-CON. Can I come right down?”

Let’s talk rodenticides. That’s the fancy word for chemicals that kill rodents, particularly rats and mice. For many decades, the most ubiquitous rodenticide marketed was warfarin, an anticoagulant. When rodents like Jerry ate warfarin, it prevented their blood from clotting, resulting ultimately in death by hemorrhage. But eventually Jerry developed some resistance to warfarin, so the pesticide companies developed bigger, badder, second-generation anticoagulant rodenticides. These were more potent and longer-acting, but still had basically the same mechanism — interfering with normal blood clotting. The good news was that as long as we got to Snoopy soon after ingestion and as long as we knew it was any of these anticoagulants, treatment was relatively easy: Induce vomiting to remove as much product as possible from his system. Dose with activated charcoal to minimize further absorption of any poison remaining in his gut. Finally, prescribe oral Vitamin K, which works as an antidote.

The length of time Snoopy needs to take Vitamin K after ingesting anticoagulant rodenticides can range from two to four weeks, depending on the particular product. That’s one reason we want to know the exact active ingredient. Second-generation anticoagulant rodenticides last in the system a whole lot longer than warfarin. These products include such chemicals as diphacinone, difethialone, chlorophacinone, brodifacoum, and bromadiolone. Not exactly catchy names. So these products have been marketed under such brand names as Havoc, Just One Bite, and, of course, d-CON. Regardless of the brand name, treatment for accidental pet ingestion of any anticoagulant rodenticide is basically the same.

Here’s where we come to today’s breaking news. In the past, the brand name d-CON was virtually synonymous with anticoagulant rodenticide. That is about to change. d-CON is now marketing a product under the same name, but with a completely different active ingredient, a completely different mode of action, and a completely different treatment for accidental ingestion by pets. Why are they changing the product? Well, it seems the EPA has new regulations restricting the residential use of the long-acting second-generation anticoagulants rodenticides. The makers of d-CON have had to come up with something else to sell that wasn’t a second-generation anticoagulant, but was still effective against warfarin-resistant rodents.

One option was a chemical called bromethalin. This is one nasty poison, a neurotoxin causing hyperexcitability, seizures, and, virtually always, death. It has no antidote. I have seen only one animal, a small dog, die from bromethalin toxicity. It has terrified me ever since. I applaud the makers of d-CON for recognizing the danger such a product poses not just to pets but to children, and opting to take a different tack. Not all companies are being that thoughtful, so I am putting out my two cents here, and asking you all to read labels carefully and never buy or use any rodenticide containing bromethalin.

Which brings us to what will eventually be your only other chemical alternative for rodent control: Cholecalciferol. Cholecalciferol is another name for vitamin D3. How can a vitamin be poisonous, you ask? Easy. At normal doses, cholecalciferol functions to help the body retain calcium, but in large doses (such as in the new d-CON) cholecalciferol leads to lethally high calcium and phosphorus levels that cause kidney failure and death within two to three days. On the up side, the new bait is relatively easy to identify. It has a different texture and appearance from the old green or red blocks of anticoagulant. Called “soft bait,” it has a consistency more like Play-Doh. On the down side, the new product is so concentrated that eating relatively small amounts may be deadly to cats and dogs. Clinical signs may not appear until several days after ingestion, and may include excessive drinking and urination, vomiting, loss of appetite, weakness, and lethargy. By the time pets are symptomatic, it is often too late to save them. Treatment can involve weeks of aggressive intravenous fluid therapy and monitoring, and pets that survive may have permanent kidney and other organ damage.

Here are the important steps you can take to protect Snoopy, while continuing to wage war against Jerry. First, if you must use chemical rodenticides, do not use bromethalin. Whatever product you use, make sure you know exactly what it is. Save all packaging so your veterinarian can identify the active ingredient and concentration if Snoopy accidentally takes the bait. Many folks have older products stashed away in their shed or garage for years, so never assume you know what the active ingredient is. Use “pet-resistant” boxes to hold any bait you put out, but don’t assume a determined Snoopy can’t chew through that box. Secure any “refill” bait packages in dog-proof containers. Finally, if Snoopy does ingest any rodenticide, do not wait. Call your veterinarian immediately. Grab the packaging to bring with you. Then, yes, you can come right down!