Mouse and rat poisons: Anticoagulant rodenticides
The bottom line
Pesticides used to kill mice, rats, and other rodents are called rodenticides. They can also harm humans. Anticoagulant rodenticides can cause bleeding if they are eaten in large amounts or repeatedly.
Prevention Tips
Place bait and bait stations where children and pets cannot see or reach them.
Choose a rodenticide that is designed for use at home; place it according to label instructions.
If you find old mouse and rat poisons around your home or property, contact your local hazardous waste disposal facility to find out how to dispose of them safely.
This Really Happened
A 36-month-old girl was admitted to a hospital because she was bleeding from her nose and mouth and had experienced extensive bruising during the preceding week. The first urine she passed in the hospital was bloody. Lab tests showed that the girl had lost a lot of blood and that her blood would not clot normally. She was given fresh frozen plasma (a source of clotting factors), packed red blood cells, and IV vitamin K. When asked about the presence of blood thinners or rat poison in the home, the girl’s mother said that she had used a brodifacoum-containing rodenticide during the preceding month. Brodifacoum was detected in the girl’s blood.
The girl was allowed to go home, and her mother was to give her oral vitamin K. Lab tests done 2 days later showed that inadequate blood clotting had returned because the mother had failed to give the girl the vitamin K. The girl was readmitted to the hospital a week later with inadequate clotting again due to her mother’s failure to give vitamin K. After 3 days in the hospital, the girl was discharged on oral vitamin K in the care of her aunt with child protective agency monitoring. The girl continued to receive oral vitamin K because brodifacoum was still found in her blood on day 102. No brodifacoum was detected on days 116 and 151. The girl was lost to follow-up after day 151 because the family moved away (from Travis et al., 1993).
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What are anticoagulant rodenticides?
Rodenticides are intended to kill unwanted rodents, particularly rats and mice. Anticoagulant rodenticides are similar to warfarin, which is a medication used to reduce blood clotting in people with conditions in which clots form within the circulatory system (thrombosis). This also increases the risk of clots breaking free (emboli) and blocking blood flow to vital organs.
Warfarin has been used as an anticoagulant rodenticide, but some rodents have become resistant to its effects. This led to the development of “superwarfarins,” which are more powerful. Examples include brodifacoum, bromadialone, diphacinone, and difethialone.
How do anticoagulant rodenticides work?
Anticoagulant rodenticides work by preventing a rodent’s blood from clotting. This leads to internal bleeding and the death of the rodent. Anticoagulant rodenticides accomplish this by interfering with the action of vitamin K to activate clotting factors made by the liver for an extended period of time.
Are anticoagulant rodenticides deadly for humans?
Humans’ blood clotting system functions similarly to that of rodents, so humans swallowing an anticoagulant rodenticide are likewise in danger of bleeding. Fortunately, people are much bigger than rodents, so the same amount of anticoagulant rodenticide results in a much lower concentration in a person and, therefore, much less anticoagulant action.
Most small ingestions, like a toddler tasting a product, do not result in symptoms. Large or repeated ingestions, however, can result in impaired blood clotting and bleeding. The most common bleeding sites are the gums, urinary tract, nose, and gastrointestinal tract. The most frequent type of bleeding reported in the few cases of deaths from superwarfarins is bleeding in the brain.
How is anticoagulant rodenticide poisoning treated?
Since anticoagulant rodenticides block the action of vitamin K on clotting factors, initial treatment of bleeding usually includes giving IV clotting factors. At the same time, vitamin K treatment is provided until blood clotting returns to normal. With superwarfarin poisoning, vitamin K treatment might be necessary for months.
Can anticoagulant rodenticides harm the skin or eyes?
Anticoagulant rodenticide products are mostly made as pellets or blocks. The dust from them can be mildly irritating to the skin and eyes. Handling any sort of pesticide should be followed by thorough handwashing with soap and water. Affected eyes should be irrigated with warm water.
How to prevent anticoagulant rodenticide poisoning in humans
The best way to prevent anticoagulant rodenticide poisoning is to limit their use. If possible, use traps rather than poisons to capture rodents. Consider opting for products using bait stations, where the rodenticide is difficult for children to access.
Make it hard for rodents to enter your home by plugging gaps around all exterior openings and using weather-stripping on doors and windows. Keep trash container lids tight, do not leave pet food out, and avoid feeding birds if rodents are a problem in your neighborhood.
The US Environmental Protection Agency requires the addition of a bittering agent and indicator dye to all anticoagulant rodenticides. The bittering agent provides a bad taste intended to limit the amount of product a child might eat (rodents are not bothered by it). The dye can help identify whether a child has handled or eaten any of the product. It is not known whether bittering agents are an effective way to limit the amount of rodenticide swallowed.
Treating someone who swallows a rodenticide
Clear out the mouth and give a small amount of water or milk to drink.
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