Rodenticide Toxicity

Updated: Oct 14, 2019
  • Author: Derrick Lung, MD, MPH; Chief Editor: Asim Tarabar, MD  more...
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Overview

Practice Essentials

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. Before the mid-20th century, heavy metals (arsenic, thallium) were the often-used agents. (See Etiology, Presentation, and Workup.)

Since the mid-20th century, anticoagulant substances have been the mainstays of rodenticide products. In 2017, anticoagulant rodenticides constituted 5185 of the 8930 case mentions of exposure to rodenticides recorded in the National Poison Data System (NPDS), administered by the American Association of Poison Control Centers (AAPCC). (See Epidemiology.) [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.

Alpha naphthyl thiourea

Alpha naphthyl thiourea (ANTU, Dirax) is a rodenticide that can cause pulmonary edema.

Strychnine

Strychnine is a plant alkaloid that, in the past, was used widely as a rodenticide. This agent is not used much today. Consider strychnine toxicity if an individual presents with a generalized seizure-like appearance but without loss of consciousness or extensor posturing with risus sardonicus. Strychnine has been discovered as an adulterant in some street drugs (cocaine, heroin, amphetamines). [2, 3]  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 developing countries where this product is still used as a rodenticide. Consider thallium toxicity when treating a patient with painful neuropathy and hair loss. Cases of thallium poisoning associated with malicious criminal activity have been reported in the United States.

Arsenic

Arsenic was widely used as a rodenticide until the late 20th century. It may still be found in liquid form in old barns and storage sites.

Barium-containing rodenticides

Worldwide, barium toxicity continues to be occasionally reported. Profound hypokalemia is the most characteristic effect, in addition to abdominal pain, nausea and vomiting, and altered mental status. No commercially available barium-containing rodenticides are currently available in the United States, so exposures are sporadic. The most recent published case of barium toxicity encountered in the United States was due to ingestion of fireworks. [4]

Bromethalin

Bromethalin, which is a neurotoxin, is increasingly used as an alternative to long-acting anticoagulant and cholecalciferol rodenticides. In 2017, AAPCC-NPDS reported 1132 single exposures, with 856 in children aged less than 6 years. [1]  The prognosis for most accidental ingestions appears to be excellent and the effects are generally self-limited. However, a reported ingestion of 17 mg of bromethalin in an adult resulted in altered mental status, increased cerebrospinal fluid pressure, cerebral edema, and death. [5]   

Cholecalciferol-containing rodenticides

Cholecalciferol-containing rodenticides produce hypercalcemia. However, overdoses are not likely to occur with this type of rodenticide because they require extremely large doses to cause toxicity in humans.

Yellow phosphorus

Yellow phosphorus was once used as a rat or roach poison. Exposure to this highly combustible toxin can cause signs and symptoms including a garlic odor, oral burns, vomiting, and phosphorescent, smoking feces.

Warfarin-type anticoagulants

Most rodenticides encountered today are the warfarin-type anticoagulants and the long-acting brodifacoum anticoagulant products. In the United States and various other parts of the world, the long-acting products (known as superwarfarins) have become the most common rodenticide encountered. [1]  In compliance with the 2008 Environmental Protection Agency (EPA) ban on certain rodenticides, in the United States, the last consumer-marketed long-acting anticoagulant rodenticides were produced in 2015. However, pest control professionals can continue to obtain these products. And, as shown by the annual poison center reports, significant numbers of exposures continue to occur, years after these products' discontinuation.

The prolonged anticoagulant effect of superwarfarins presents a challenging and deadly poisoning to manage. In fact, deaths from rodenticide appear to be rare but are almost always associated with exposure to long-acting anticoagulants. 

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. [6, 7]

Patient education

For patient education information, see Poisoning Treatment and Child Safety Proofing.

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Etiology

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:

  • Disrupt 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 phosphorus)
  • Combine with sulfhydryl groups, thus blocking numerous enzymatic reactions and cell signaling pathways (eg, arsenic)
  • Destroy red blood cells (RBCs) 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 (eg, warfarin, superwarfarins)
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Epidemiology

In 2017, the AAPCC reported a total of 8494 single exposures to rodenticides to US poison control centers. Of those, 4810 were to long-acting anticoagulant rodenticides, 187 were to warfarin-type anticoagulant rodenticide, and 1132 were to bbromethalin rodenticides. The outcome of rodenticide exposures was generally benign; overall, 7 exposures resulted in major outcomes, and 2 deaths occurred. Of all the exposures reported, 6604 involved children younger than 6 years. [1]  

The vast majority of exposed individuals were children younger than age 6 years, in which case, the exposure was most often unconfirmed. Eighty percent of the long-acting anticoagulant exposures were in children younger than 6 years. [1]

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, from 1999-2003 revealed that rodenticides were involved in 2.5% of all human exposures, or 3.4% of exposures when pharmaceuticals were removed from the sample. Children younger than age 5 years incurred 31% of rodenticide exposures in SINITOX. Twenty-three exposures resulted in death; 20 of these were intentional suicides. [8]

In China, banned tetramethylene disulphotetramine (TMDT) was responsible for 14,000 poisonings with 932 deaths between January 1991 and December 2010. [9]

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Prognosis

As long as the proper duration of therapy is used, acute overdoses of anticoagulant rodenticides generally resolve uneventfully. [10] Deaths usually occur when patients present well after exposure when severe sequelae of anticoagulation have already manifested. Patients exposed to herbal-based rodenticides, such as red squill, usually present with only gastrointestinal (GI) symptoms, which are also easy to treat, and full recovery is expected.

Metal rodenticides produce serious toxicity and many produce long-term sequelae. Thallium and arsenic are responsible for severe peripheral neuropathies, and fatalities have occurred; thus, the prognosis is guarded and depends on the speed of response.

PNU produces a permanent insulin-dependency syndrome. An autonomic neuropathy is not unusual, further complicating the therapy of diabetes.

Fluoroacetate and zinc phosphide intoxications are potentially fatal. With no true antidote therapy, the mortality rate is considerable. Phosphorus intoxication produces serious corrosive injuries and may require extensive reconstructive surgery.

With anticoagulant rodenticides, the following complications have been reported:

  • Spontaneous intra-abdominal hemorrhage
  • Hematuria
  • Hematemesis
  • Spontaneous hemoperitoneum
  • Intracerebral hemorrhage
  • Death

 

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