A 15-year-old Wisconsin boy has been charged with attempted murder for slipping mouse poison into his family's food over a five-week period. His mother, stepfather, and 3-year-old half-sister suffered a variety of nonlethal symptoms, including stomach pains and vomiting. The alleged perpetrator has told police that he didn't intend to kill his family, just to make them ill. How much mouse poison can a human ingest without dying?
Quite a bit, if it's the kind this troubled Wisconsin teen allegedly employed and if medical care is administered in a timely fashion. The mouse poison in question was reportedly the d-Con brand; d-Con's active ingredient is brodifacoum. This substance is classified as a superwarfarin, a family of potent, long-acting anticoagulants, or blood thinners. It is a relative of warfarin, an anticoagulant discovered in the 1940s by the Wisconsin Alumni Research Foundation; the foundation's scientists found the chemical in spoiled sweet-clover hay, which was causing fatal hemorrhaging in some cattle. Warfarin is still used today to prevent blood clots.
Brodifacoum causes death in mice by thinning their blood so much that they hemorrhage. Products like d-Con mouse poison use brodifacoum because it doesn't cause immediate death; as a result, mice are unable to associate the bait traps with their peers' demise and keep going back for more. Also, because brodifacoum causes an unslakable thirst, mice often venture outside in search of water just before they die—which leaves homeowners with fewer rodent carcasses festering in their walls.
There is no consensus on how much brodifacoum constitutes a lethal dose for humans; there simply haven't been enough cases of brodifacoum poisoning for medical researchers to study. Toxicity depends not only on how much has been ingested but on the ingester's weight, health, and various other factors. According to a monograph from the International Programme on Chemical Safety, however, there have been a few isolated cases of people surviving extremely large doses. In 1984, for example, a disturbed pregnant woman was admitted to a hospital after ingesting 75 milligrams of brodifacoum over two days. That's equivalent to a whopping 50 ounces of d-Con mouse poison. She survived, although she suffered severe hemorrhaging throughout her body and lost her baby.
A much smaller dose of just a few milligrams could theoretically be fatal, but only if no medical attention was given. Fortunately, the antidote to brodifacoum is the readily available vitamin K1. Ten milligrams to 20 milligrams of vitamin K1 usually does the trick, followed by regular 5 milligram doses for the next month if necessary. In worst-case scenarios, a blood transfusion may also be necessary. (Information on the Wisconsin family's treatment has not been released to the public.)
Though there is little data on lethal-dose levels for humans, much more is known about how much brodifacoum is necessary to kill a dog. Pets, unfortunately, frequently eat rodenticides, so veterinarians have years of experience caring for accidentally poisoned canines. The rule of thumb for dogs is that a lethal dose consists of between 0.2 and 4 milligrams of brodifacoum for every kilogram of body weight. So, a 75-pound dog would need to eat more than 4 ounces of d-Con mouse poison to approach the bottom end of that range.