One Pill Can Kill: Superwarfarins

It’s a quiet Sunday afternoon as you and your partner drive around enjoying the fall colors. Your truck has been deep-cleaned, your fuel tank filled, and you’re just about to grab a midshift coffee when your dispatcher breaks the silence.

“Two-year-old child, alert and oriented, mother observed him eat rat poison.”

The address that pops up on your dashboard CAD screen is a full 20 minutes away—turns out you were the only truck in the region experiencing a quiet Sunday. You pull a U-turn and proceed, ultimately arriving at a detached brick home where you’re met at the front door by anxious parents. They tell you their child—who was born with a ventricular septal defect that was repaired at age five months at the children’s hospital 50 miles away—was observed to eat a pellet of rat poison about 30 minutes ago. They searched the brand and were horrified to read that 10,000 children are poisoned each year by this “superwarfarin.” They hand you the container, which reads brodifacoum. While you may not have heard of brodifacoum, you have certainly heard of warfarin!

A quick pediatric triangle assessment of appearance, work of breathing, and perfusion is normal. You decide to load up.

Pop quiz: This child had infant heart surgery at a children’s hospital and presents with brodifacoum ingestion. Should you go to:

• Your local ER (a 10-minute drive)?
• Your pediatric ER (a 30-minute drive)?
• The child’s tertiary-care children’s hospital (a 50-minute drive)?

En route your exam reveals a healthy child with normal vitals and no physical complaints. You note a green tinge to the child’s lips that is distinct from cyanosis.

At the ER the triage nurse seems unimpressed; he asks you to offload the child to the waiting room. First you help the family find a patient washroom. Upon exiting the father looks panicked and asks you to look at the child’s stool in the toilet bowl. It’s greenish.

You inform the triage nurse, whose interest is piqued, and the child is sent to a fast-track area of the department.

Brodifacoum and Other Superwarfarins

Warfarin has been used as a pesticide for more than 50 years. Concerns around warfarin resistance led to the creation of superwarfarins, which work similarly but last much longer—months instead of hours. This drug class includes brodifacoum, bromadiolone, difenacoum, and flocoumafen and makes up the great majority of rat poisons on the domestic market.¹ These drugs are vitamin K antagonists and prevent vitamin K from activating dependent clotting factors. I’ll spare you the horrors of the clotting cascade, but suffice to say without vitamin K, you won’t get thrombin, and without thrombin, you won’t get a stable clot. Rats bleed to death. (Other less common rat poisons contain red squill, which is a digoxin substance, strychnine, and phosphorus.)

But very few children have severe toxicity, especially when only a small amount of poison is consumed. In a 2006 study of 68,000 children under 6 years old who consumed rat poisons, more than a third visited a healthcare facility, but only 302 were hospitalized and 219 admitted to an intensive care unit.² In a registry study of poison control centers, 10,762 pediatric cases of unintentional ingestions of brodifacoum were reviewed; 67 patients reported coagulopathy, but no major effects or deaths occurred.³ In a study of 545 children who ingested rat poison, none had significant coagulopathy on blood work; two had non-life-threatening nosebleeds.⁴ The authors concluded that ingestions of less than one box (and most are only a pellet or two) need no treatment or follow-up.

Large toxicities are another matter. In a case report, a 25-year-old attempted suicide by ingesting four boxes of superwarfarin, each 42 g of bait (0.005% brodifacoum).⁵ Nine days later he presented to an emergency room after syncope and had hematochezia, gross hematuria, epistaxis, anemia, and severe coagulopathy; imaging revealed pleural, pericardial, and mediastinal bleeding. He was given vitamin K and fresh frozen plasma, which contains clotting factors, and discharged on oral vitamin K. Fifteen weeks later he returned with a history of additional ingestion. Neurologic status was initially normal, but he became comatose after induction of vomiting with ipecac. He died of subarachnoid hemorrhage.

Back to the Case

After 30 minutes of chatting with colleagues and clearing your stretcher, you pull out of the ambulance bay and are surprised to see your little kiddo strolling out of the ER with both parents.

Serious complications and death from superwarfarin are very rare and dose-dependent. Prehospital providers should rest assured that small ingestions of rat poison are not dangerous. Expert counseling and follow-up can be offered by emergency doctors, family doctors, pediatricians, and poison-control centers. Reassurance and referral to experts who can guide in watching for signs of serious toxicity in the days that follow the ingestion are all that is required for small overdoses. Signs that would warrant expert attention include bruising and bleeding in stool, urine, or gumlines. Large overdoses will often prompt blood work in the emergency department, with observation lengths varying with coagulation studies.

You rightly choose to go to your local hospital. Not that you need to go to the closest, but the pediatric ER and tertiary-care center offer no additional benefit to your patient, and the past surgical history in this case is irrelevant, as no increased risk of bleeding is present this far after surgery.

Sidebar: Public Health vs. Public Health

Unintentional rat poison ingestions are preventable, but doing away with rat poison altogether causes additional concerns. To be sure, rat infestations are bad. Public health officials work hard to control rats, as they, and the insects that live on them, can spread diseases like bubonic plague,⁶ hemorrhagic fever, leptospirosis, salmonellosis, and rat bite fever.

But the frequency with which young children consume rat poisons has raised red flags for years, particularly at the Environmental Protection Agency. The EPA has been monitoring human ingestions of rat poisons since the 1970s and believes they are four times as common as reported to poison centers. In 1998 the EPA declared that rat poisons must taste bitter and be dyed bright colors so their consumption would be obvious (this is why the child in this case had a green bowel movement). Yet legislative tug-of-wars went on for over a decade, and those recommendations didn’t always stick. A Scientific American investigation found the issue has never fully been resolved.²

References

1. Kanabar D, Volans G. Accidental superwarfarin poisoning in children—less treatment is better. Lancet, 2002 Sep 28; www.thelancet.com/journals/lancet/article/PIIS0140-6736(02)11120-2/fulltext.

2. McClure R. Rat Poisons Endanger 10,000 Children Every Year in the U.S. Scientific American, 2010 Dec 14; www.scientificamerican.com/article/rat-poisons-endanger-10000-children/.

3. Shepherd G, Klein-Schwartz W, Anderson BD. Acute, unintentional pediatric brodifacoum ingestions. Pediatr Emerg Care, 2002 Jun; 18(3): 174–8.

4. Ingels M, Lai C, Tai W, et al. A prospective study of acute, unintentional, pediatric superwarfarin ingestions managed without decontamination. Ann Emerg Med, 2002 Jul; 40(1): 73–8.

5. Kruse JA, Carlson RW. Fatal rodenticide poisoning with brodifacoum. Ann Emerg Med, 1992 Mar; 21(3): 331–6.

6. Bigham B. Plague: Four Things You Need to Know. EMS World, 2017 Nov 3; www.hmpgloballearningnetwork.com/site/emsworld/article/219160/plague-four-things-you-need-know.

After a decade working as a helicopter paramedic, Blair Bigham, MD, MSc, EMT-P, completed medical school in Ontario, Canada, where he is now a resident physician in the emergency department. He has authored over 30 scientific articles, led major national projects to advance prehospital research and participated in multiple collaboratives, including the Resuscitation Outcomes Consortium.