Rodenticide Toxicity 

Updated: Dec 29, 2015
Author: Derrick Lung, MD, MPH; Chief Editor: Asim Tarabar, MD 

Overview

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. 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 2014, anticoagulant rodenticides constituted 8833 of the 11,309 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]

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 cause toxicity in humans.

Yellow phosphorus

Yellow phosphorous 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, 5]

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. In 2011, NPDS reported 2 such deaths and 39 patients experiencing moderate and 15 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.[6, 7]

Patient education

For patient education information, see the First Aid and Injuries Center, as well as Activated Charcoal, and Poison Proofing Your Home.

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:

  • 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 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)

Epidemiology

The predominant rodenticide exposure is anticoagulant rodenticides, generally the superwarfarin type. In 2014, the AAPCC reported a total of 10,823 single exposures to rodenticides to US poison control centers. Of these, 8372 were to long-acting anticoagulant rodenticides, and 181 were to warfarin type anticoagulant rodenticides. The outcome of rodenticide exposures was generally benign; overall, 12 exposures resulted in major outcomes, and six deaths occurred. Of all the exposures reported, 8809 involved children younger than 6 years.[1]

International occurrence

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]

Prognosis

As long as the proper duration of therapy is used, acute anticoagulant rodenticide overdoses generally resolve uneventfully.[9] Deaths usually occur when patients present well after exposure when severe sequelae of anticoagulation have already manifested. Exposures 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.

Complications

With anticoagulant rodenticides, the following complications have been reported:

  • Spontaneous intra-abdominal hemorrhage

  • Hematuria

  • Hematemesis

  • Spontaneous hemoperitoneum

  • Intracerebral hemorrhage

  • Death

Morbidity and mortality

The vast majority of rodenticide exposures are to anticoagulants. According to the 2014 NPDS data, among all rodenticide exposures, 76% of persons treated in a health care facility were exposed to the long-acting superwarfarins. The superwarfarin-exposed individuals experienced 37 moderate and 11 major effects and three deaths. The warfarin-exposed group (181 patients) had one individual experiencing moderate effects, and no major effects or deaths.[1]

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

 

Presentation

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 ingestion may not have actually occurred or that it has 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. Surreptitious poisoning may occur from exposure to adulterated or contaminated drugs of abuse. The presence of anticoagulation may represent Munchausen syndrome.

Common presenting symptoms after exposure to long-acting anticoagulants include the following:

  • Flank pain with or without frank hematuria

  • Excess bleeding or bruising after relatively minor or no apparent trauma

  • Hemoptysis

  • Epistaxis

  • Menorrhagia

An organophosphate rodenticide known as TresPasitos, made with the chemical aldicarb and sold illegally in the United States, has been used primarily by Hispanic individuals.[10] People who ingest this toxin may present with symptoms of acetyl cholinesterase inhibition.

Additional presentations of rodenticide exposure include the following:

  • Barium - May cause headache, weakness, nausea, abdominal pain, or shortness of breath

  • PNU - May cause complaints of nausea, vomiting, abdominal pain, or dizziness

  • Thallium - Exposed individuals may report acute GI distress and subsequent anorexia, myalgias, painful neuropathy, and hair loss

  • Strychnine - May cause anxiety, muscle twitching, or uncontrolled facial grimacing

  • Zinc phosphide - Inhalation leads to marked shortness of breath as pulmonary edema develops

  • Arsenic - High doses cause nausea, vomiting, bloody diarrhea, and garlic taste in the mouth

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.

Physical Examination

Anticoagulant rodenticides rarely produce symptoms at all; when they do, however, 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.

  • PNU - Odor of peanuts

  • Zinc phosphide - Smells of rotting fish

  • Organophosphates, such as Tres Pasitos - Smell like garlic

 

DDx

Diagnostic Considerations

Congenital deficiency in clotting factor VII may present with bleeding associated with an abnormal prothrombin time (PT) but a normal activated partial thromboplastin time (aPTT). At first, this may appear to be anticoagulation from a rodenticide or Coumadin; however, with the marked prolongation in PT, some abnormality in aPTT should be present, except in specific factor VII deficiency.

Conditions to consider in the differential diagnosis of rodenticide exposure include the following:

  • Acute Respiratory Distress Syndrome

  • Ammonia toxicity

  • Arsenic toxicity

  • Chlorine Gas toxicity

  • Clonidine toxicity

  • Cyanide toxicity

  • Fluoride toxicity

  • Hydrogen Sulfide toxicity

Differential Diagnoses

 

Workup

Approach Considerations

Obtain the following tests in patients with possible rodenticide poisoning:

  • Glucose (point-of-care) - In every patient with altered mental status

  • Electrolytes, serum glucose level, and ketones – Profound abnormalities may suggest exposure to uncommon rodenticides such as barium, cholecalciferol, or PNU.

  • Pregnancy tests - In women of childbearing age

  • Serum acetaminophen level - In every intentional exposure

  • Complete blood count (CBC) - In patients with evidence of bleeding or hemolysis

  • Creatine phosphokinase (CPK) and lactic acid - In patients suspected of exposure to strychnine

Measure prothrombin time (PT), international normalized ratio (INR), and activated partial thromboplastin time (aPTT) if the ingested substance is an anticoagulant. Possibly consider bleeding time and platelet count measurements in patients with evidence of bleeding. If available, measurement of quantitative coagulation factors may be helpful, and these may be available far before actual analysis for suspect anticoagulant levels. Coagulation studies are expected to be normal in acute exposures to anticoagulants. These patients may require serial testing for 2 days to rule out or confirm toxicity. Abnormal measurements on initial testing suggest the possibility of long-term exposure.

Because the availability of RBC cholinesterase is so poor, do not depend on supporting laboratory evidence when an exposure to an organophosphate-containing substance is suspected.

Laboratory verification of the anticoagulant rodenticides (eg, brodifacoum, difenacoum) is available; however, the result takes several days and is not necessary to guide therapy. Serial levels might only be helpful to estimate the drug half-life and duration of required therapy. In addition, blood tests for arsenic, thallium, mercury, and lead may be useful but are usually considerably time consuming.

Abdominal plain film radiography

If a metal rodenticide (eg, thallium, arsenic, barium) is considered, obtaining an abdominal plain film radiograph may be helpful, because these metals are radio-opaque.

Consultations

Consult with the regional poison control center or a medical toxicologist for additional information and patient care recommendations.

Obtain a psychiatric evaluation if the ingestion was intentional. Consult a hematologist or a medical toxicologist for long-term follow-up if a long-acting anticoagulant was ingested.

Monitoring

Patients who ingest anticoagulant rodenticides and are discharged when their clotting studies are found to be normal may have delayed symptom onset and may continue to ingest the rodenticide once they are discharged. In these cases, the treating physician is responsible for proving that any sequelae are not the result of a missed opportunity to treat. As previously stated, consult a hematologist or a medical toxicologist for long-term follow-up if a long-acting anticoagulant was ingested.

 

Treatment

Approach Considerations

For small, unintentional ingestions of an anticoagulant rodenticide, repeat PT measurements 24 and 48 hours post ingestion to ensure that no effects on the coagulation pathway are present. This may be done on an outpatient basis if no other reason for inpatient hospitalization exists.

Intentional exposure to an anticoagulant rodenticide for suicidal or other reasons may require substantial treatment with vitamin K for a protracted period of time, particularly in the face of exposure to one of the superwarfarins (see Warfarin and Superwarfarin Toxicity). It may be wise to monitor brodifacoum levels to determine a treatment endpoint.[11] The source of exposure to a superwarfarin should be disclosed to avoid recidivism.

Prehospital Care

Points to remember in prehospital patient care for rodenticide poisoning include the following:

  • As in most poisoning situations, it is best to "scoop and run”; very little can be done in the field

  • Always look for a container, so that the specific product can be determined

  • Decontamination may be necessary for situations in which patients and their garments are contaminated with the pesticide

  • Administer benzodiazepines in patients with seizurelike activity

  • Secure airway and place intravenous (IV) lines in hemodynamically unstable patients

Evidence-based guidelines on the management of long-acting anticoagulant rodenticide poisoning are available from the AAPCC.[12]

Emergency Department Care

Patients who present or develop renal failure may require hemodialysis. Patients with severe respiratory compromise from zinc phosphide, arsenic, or barium may require endotracheal intubation for ventilatory support.

GI evacuation is rarely useful; however, consider it for exceptional cases in which a huge overdose is suspected and in which the patient presents early to an emergency facility.

Give all patients with rodenticide overdose activated charcoal as soon as possible to prevent further absorption of ingested toxins. With anticoagulant overdoses, perform a careful physical examination to look for any sign of bleeding.

Severe hemolysis from phosphine gas (released from zinc phosphide) may require exchange transfusion of RBCs.

Other medical therapy depends on identification of specific substances involved. Examples are as follows:

  • If a heavy metal is suspected, institute chelation therapy (see Arsenic Toxicity in Emergency Medicine and Thallium Toxicity)

  • If an organophosphate is suspected, administer atropine for initial management and consider oxime use

  • Monosodium fluoroacetate and zinc phosphide have no specific antidotal therapy that has been of any consistent advantage; only supportive care is available

  • PNU induces an alloxan-like destruction of pancreatic beta cells, which may be prevented with nicotinamide

If no coagulopathy or active bleeding is found in the setting of an anticoagulant exposure, prophylactic treatment with vitamin K is absolutely contraindicated. This would potentially mask the onset and severity of an ingestion and would obfuscate the time required for clinical and/or laboratory monitoring.

If a coagulopathy is documented, but without active hemorrhage, institution of vitamin K therapy is suggested (see Warfarin and Superwarfarin Toxicity). Since all of the vitamin K–dependent clotting factors may be affected, the hemolytic factors C and S may be affected early and may cause the presentation to be one of acute thrombosis rather than anticoagulation.[13, 14]

In addition to vitamin K, prothrombin complex concentrates and/or fresh-frozen plasma may be needed to rapidly reverse anticoagulation from warfarin and superwarfarins when patients present with life-threatening hemorrhage (see Warfarin and Superwarfarin Toxicity for an extended discussion regarding treatment).

 

Medication

Medication Summary

Give all patients with rodenticide overdose activated charcoal as soon as possible to prevent further absorption of ingested toxins.

If a coagulopathy is documented, institution of vitamin K therapy is suggested. However, again, in the absence of documented coagulopathy, empiric vitamin K therapy is contraindicated. Intentional exposure to an anticoagulant rodenticide for suicidal or other reasons may require substantial treatment with very high doses of vitamin K for a protracted period of time, particularly in the face of exposure to one of the superwarfarins.

Antidotes, Other

Class Summary

Activated charcoal is empirically used to minimize systemic absorption of the toxin. It may be of benefit only if administered within 1-2 hours of rodenticide ingestion.

Neutralize the effects of the anticoagulant rodenticide-induced hemorrhages with vitamin K.

Activated charcoal (Actidose-Aqua, Char-Caps, Kerr Insta-Char)

Activated charcoal is used in the emergency treatment of poisoning caused by drugs and chemicals. A network of pores in activated charcoal adsorbs 100-1000 mg of drug per gram of charcoal. Activated charcoal does not dissolve in water.

This agent may be administered with a cathartic (eg, 70% sorbitol), except in young pediatric patients in whom electrolyte disturbances may be of concern. For maximum effect, administer activated charcoal within 30 minutes of poison ingestion.

Phytonadione (MEPHYTON)

There is no need to begin therapy unless the INR is greater than 2. No data exist to prove that such therapy prevents anticoagulation, although vitamin K therapy is shown to reverse anticoagulation once it develops. With long-acting anticoagulants, treatment may need to be at much higher doses and for a protracted period of time.