eMedicine Specialties > Emergency Medicine > Toxicology

Toxicity, Rodenticide

Author: Steven Marcus, MD, Professor, Department of Preventive Medicine and Community Health, Associate Professor, Department of Pediatrics, New Jersey Medical School, University of Medicine and Dentistry of New Jersey; Executive and Medical Director, New Jersey Poison Information and Education System; Consulting Staff, Departments of Pediatrics and Internal Medicine, University Hospital, University of Medicine and Dentistry of New Jersey; Consulting Staff, Department of Pediatrics, Newark Beth Israel Medical Center
Contributor Information and Disclosures

Updated: Oct 29, 2009

Introduction

Background

Rodenticides are a heterogeneous group of compounds that exhibit markedly different toxicities to humans and rodents. They are among the most toxic substances regularly found in homes. The varieties of rodenticides used over the years are legion, leading to the popular expression, "to build a better mousetrap." Before the mid twentieth century, heavy metals (arsenic, thallium) were the often used agents. Since the mid century, anticoagulant substances have been the mainstays of rodenticide products. In 2007, 15,405 case mentions of exposure to rodenticides were recorded in the National Poison Data System (NPDS) as administered by the American Association of Poison Control Centers.¹

Red squill

The botanical preparation of red squill, containing a cardiac glycoside as an active ingredient, was used as a rodenticide for many years. In theory, rodents ingest the product, and because they are incapable of vomiting, develop glycoside intoxication and pulmonary edema. Because humans are capable of vomiting, red squill was considered harmless, even to children. This product is not used much today because of its limited effectiveness as a rodenticide.

α-naphthyl thiourea

α-naphthyl thiourea (ANTU, Dirax) is another rodenticide that is said to produce pulmonary edema in rodents but not in higher mammals.

Strychnine

Strychnine is a plant alkaloid that, in the past, was used widely as a rodenticide. This agent is not used much today but is reported to have caused 3 deaths in 1998. Consider strychnine toxicity if an individual presents with generalized seizure like appearance but without loss of consciousness or extensor posturing with risus sardonicus. Strychnine can be found as an adulterant in some street drugs (cocaine, heroin, and amphetamines).^2,3 It is speculated that strychnine is a common contaminant in lysergic acid diethylamide (LSD). Strychnine is usually brought into the United States from other countries where its use as a rodenticide is still legal.

Thallium

Although thallium is not licensed for use in the United States, many case reports document thallium intoxications in third world countries where this product is still used as a rodenticide. Consider thallium toxicity when treating a patient with painful neuropathy and hair loss. Recent cases of thallium poisoning associated with malicious criminal activity have been reported in the United States.

Arsenic

Arsenic, the poison used in the classic play Arsenic and Old Lace, was widely used as a rodenticide until 2 decades ago. It may still be found in liquid form in old barns and storage sites. (Actually, the victims in the play were probably dispatched with strychnine not arsenic, despite the title).

Barium-containing rodenticides

Interest in these rodenticides is purely academic. No commercially available barium-containing rodenticides are currently available in the United States.

Cholecalciferol-containing rodenticides

Cholecalciferol-containing rodenticides produce hypercalcemia. However, overdoses are not likely to occur with this type of rodenticide because these products are not commonly available, and they require extremely large doses to create a toxicologic situation in humans.

Yellow phosphorus

Yellow phosphorous was once used as a rat or roach poison. Symptoms include a garlic odor, oral burns, vomiting, and phosphorescent smoking feces.

Warfarin-type anticoagulants and brodifacoum

The emergency physician should be familiar with the rodenticides used historically; however, most rodenticides encountered today are the warfarin-type anticoagulants and the long-acting brodifacoum anticoagulant products. In the United States, as elsewhere in the world, the introduction of the long-acting, also known as superwarfarin, products has become the most common rodenticide encountered. The 2007 NPDS listed 11,926 long-acting or super warfarins and 380 of warfarin-type anticoagulant rodenticide; thus, nearly 80% of all reported rodenticide exposures in 2007 were to the anticoagulant type with 97% of these the long-acting variety.¹

The long-lived nature of the anticoagulation has presented a significant and increasingly difficult to manage problem. In fact, deaths from rodenticide appear to be rare, but almost always are associated with exposure to such long-acting varieties. In 2007, NPDS reported 1 such death and 54 moderate and 10 major clinical effects.¹

Reports have been documented of rodenticide lacing of marijuana in an effort to enhance the effects. Individuals using this combination have been reported to have coagulopathies as a result.^4,5

Pathophysiology

Rodenticides that are toxic to virtually every organ system in the body have been available.

Cyanide, once prevalent but no longer used for rodenticide application, poisons the cytochrome system.

Effects of other rodenticides are as follows:

• Poison the Krebs cycle (eg, sodium monofluoroacetate)
• Destroy the pancreatic beta cell (eg, N -3-pyridylmethyl-Np -nitrophenyl urea [PNU], Vacor)
• Serve as antagonists of the neurotransmitter glycine at the postsynaptic spinal cord motor neuron (eg, strychnine)
• Drive potassium intracellularly, may lead to hypotonia (eg, barium)
• Cause chemical burns (eg, yellow phosphorous)
• Combine with sulfhydryl groups, thus blocking numerous enzymatic reactions and cell signaling pathways (eg, arsenic)
• Destroy RBC by hemolysis (eg, zinc phosphide)
• Uncouple oxidative phosphorylation (eg, bromethalin)
• Lead to vasoconstriction with ischemia (eg, norbormide)
• Block the production of vitamin K-dependent coagulation factors (more commonly found than other rodenticide applications)

The warfarinlike anticoagulants and their long-acting progeny produce toxicity by preventing the activation of vitamin K and, hence, its utilization in the production of prothrombin.

Frequency

United States

The predominant rodenticide exposures during the last few years have been anticoagulant rodenticides, generally the superwarfarin type. In 2005, the AAPCC reported a total of 18,011 reports of rodenticide exposure to US poison control centers. Of these, nearly 82% were anticoagulants and 95% of these were of the superwarfarin type. The outcome of these exposures was generally benign; however, 26 of the superwarfarin exposures resulted in a major effect and one death from such an exposure occurred. Over the past 3 years, a slight decline in such exposures has occurred, but the reports of significant morbidity in the literature seem to be increasing.

International

Aggregate tabulations for worldwide experience are not available; however, limited data are available from individual countries or regions. The report of the Brazilian National Poisoning Information System, SINITOX, revealed that rodenticides were involved in 2.5% of all human exposures or 3.4% of exposures when pharmaceuticals are removed from the sample. Children younger than 5 years incurred 31% of rodenticide exposures in SINITOX. Twenty-three exposures resulted in death; 20 of these were intentional suicides.

Mortality/Morbidity

• The vast majority of rodenticide exposures are to anticoagulants.
• According to the 2007 NPDS data, of the warfarin-type rodenticide exposures, 28% were treated in a health care facility; 75% of those hospitalized were exposures to the long-acting superwarfarins. These later individuals experienced 64 moderate or major effects and 1 death, while the warfarin-exposed group had no individuals with any more than minor effects.¹
• The vast majority of exposed individuals were children younger than 6 years, in which case, the exposure was most often unconfirmed. Eighty-eight of the long-acting anticoagulant exposures were in children younger than 6 years, and 81% of the warfarin products were also the agent involved in children younger than 6 years.¹

Race

No scientific data indicate that outcomes of exposure to any of the rodenticides are based on race.

Sex

No scientific data indicate that outcomes of exposure to any of the rodenticides are based on sex.

Age

According to the 2007 AAPCC annual report, 81% of the rodenticide exposures occurred in children younger than 6 years.¹

Clinical

History

• Many of the patients presenting with rodenticide ingestions are children who ingest such substances unintentionally and, thus, usually ingest small quantities. The literature relating to such ingestions is prone to the bias that an ingestion may not have actually occurred or it occurred at such a low dose as to be inconsequential. Thus, determining the treatment of a child based on published literature is potentially dangerous.
• Adults who ingest such substances are most likely attempting suicide; however, poisoning homicides may occur with these agents because of their ready availability. The presence of anticoagulation might represent Munchausen syndrome.
• There is a report that it is "common practice" to "lace marijuana and normal tobacco cigarettes with rodenticide in order to achieve a prolonged high." Thus, individuals may present with a clinical picture suggesting an anticoagulant overdose but deny intentional exposure.^4,5
• Common presenting symptoms after exposure to long-acting anticoagulants include
  • Flank pain with or without frank hematuria
  • Excess bleeding or bruising after relatively minor or no apparent trauma
  • Hemoptysis
  • Epistaxis
  • Menorrhagia
• Verifying the specific rodenticide is important.
  • In the United States, the rodenticide is most likely an anticoagulant.
  • Quite a few of the other rodenticides have been used over the years but are currently not popular.
  • Recently, a new rodenticide called Tres Pasitos has been found, used primarily by Hispanic individuals.⁶ People who ingest these products may present with symptoms of acetyl cholinesterase inhibition.
  • Barium may cause headache, weakness, nausea, abdominal pain, or shortness of breath.
  • Vacor (ie, PNU) may cause people to complain of nausea, vomiting, abdominal pain, or dizziness.
  • Individuals exposed to thallium may report acute GI distress and subsequent anorexia, myalgias, painful neuropathy, and hair loss.
  • Those ingesting strychnine may report anxiety, muscle twitching, or uncontrolled facial grimacing.
  • Zinc phosphide inhalation leads to marked shortness of breath as pulmonary edema develops.
  • High doses of arsenic cause nausea, vomiting, bloody diarrhea, and garlic taste in the mouth.

Physical

• Anticoagulant rodenticides rarely produce symptoms at all; however, when they do, symptoms are usually delayed. Evidence of frank bleeding, bruising, or other coagulopathy may be present if a significant exposure has occurred. The presence of petechiae under a blood pressure cuff may alert the nursing staff or ED physician to such coagulopathy.
• Characteristic odors are associated with certain rodenticides.
  • Vacor has an odor of peanuts.
  • Zinc phosphide smells of rotting fish.
  • Organophosphates, such as " tres pasitos, " smell like garlic.

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