Poisoning is contact with a substance that results in toxicity. Symptoms vary, but certain common syndromes may suggest particular classes of poisons. Diagnosis is primarily clinical, but for some poisonings, blood and urine tests can help. Treatment is supportive for most poisonings; specific antidotes are necessary for a few. Prevention includes labeling drug containers clearly and keeping poisons out of the reach of children.
Most poisonings are dose-related. Dose is determined by concentration over time. Toxicity may result from exposure to excess amounts of normally nontoxic substances. Some poisonings result from exposure to substances that are poisonous at all doses. Poisoning is distinguished from hypersensitivity and idiosyncratic reactions, which are unpredictable and not dose-related, and from intolerance, which is a toxic reaction to a usually nontoxic dose of a substance.
Poisoning is commonly due to ingestion but can result from injection, inhalation, or exposure of body surfaces (eg, skin, eye, mucous membranes). Many commonly ingested nonfood substances are generally nontoxic (see the following table); however, almost any substance can be toxic if ingested in excessive amounts.
Accidental poisoning is common among young children, who are curious and ingest items indiscriminately despite noxious tastes and odors; usually, only a single substance is involved. Poisoning is also common among older children, adolescents, and adults attempting suicide; multiple drugs, including alcohol, , and other over-the-counter (OTC) drugs, may be involved. Accidental poisoning may occur in older people because of confusion, poor eyesight, mental impairment, or multiple prescriptions of the same drug by different physicians (see also Drug-Related Problems in Older Adults).
Occasionally, people are poisoned by someone who intends to kill or disable them (eg, to rape or rob them). Drugs used to disable (eg, , benzodiazepines, gamma-hydroxybutyrate) tend to have sedative or amnestic properties or both. Rarely, parents, who may have some medical knowledge, poison their children because of unclear psychiatric reasons or a desire to cause illness and thus gain medical attention (a disorder called factitious disorder imposed on another [formerly called Munchausen syndrome by proxy]).
bezoars) in the GI tract, where they tend to remain, continuing to be absorbed and causing toxicity.
Symptoms and Signs of Poisoning
Symptoms and signs of poisoning vary depending on the substance (see table Symptoms and Treatment of Specific Poisons). Also, different patients poisoned with the same substance may present with very different symptoms. However, 6 clusters of symptoms (toxic syndromes, or toxidromes) occur commonly and may suggest particular classes of substances (see table Common Toxic Syndromes). Patients who ingest multiple substances are less likely to have symptoms characteristic of a single substance.
Symptoms typically begin soon after contact but, with certain poisons, are delayed. The delay may occur because only a metabolite is toxic rather than the parent substance (eg, methanol, ethylene glycol, hepatotoxins). Ingestion of hepatotoxins (eg, , iron, Amanita phalloides mushrooms) may cause acute liver failure that occurs one to a few days later. With metals or hydrocarbon solvents, symptoms typically occur only after chronic exposure to the toxin.
Ingested and absorbed toxins generally cause systemic symptoms. Caustics and corrosive liquids damage mainly the mucous membranes of the gastrointestinal (GI) tract, causing stomatitis, enteritis, or perforation. Some toxins (eg, alcohol, hydrocarbons) cause characteristic breath odors. Skin contact with toxins can cause various acute cutaneous symptoms (eg, rashes, pain, blistering); chronic exposure may cause dermatitis.
Inhaled toxins are likely to cause symptoms of upper airway injury if they are water-soluble (eg, chlorine, ammonia) and symptoms of lower airway injury and noncardiogenic pulmonary edema if they are less water-soluble (eg, phosgene). Inhalation of carbon monoxide, cyanide, or hydrogen sulfide gas can cause organ ischemia or cardiac or respiratory arrest. Eye contact with toxins (solid, liquid, or vapor) may damage the cornea, sclera, and lens, causing eye pain, redness, and loss of vision.
Diagnosis of Poisoning
Consideration of poisoning in patients with altered consciousness or unexplained symptoms
History from all available sources
Selective, directed testing
The first step of diagnosis of poisoning is to assess the overall status of the patient. Severe poisoning may require rapid intervention to treat airway compromise or cardiopulmonary collapse.
Poisoning may be known at presentation. It should be suspected if patients have unexplained symptoms, especially altered consciousness (which can range from agitation to somnolence to coma). If purposeful self-poisoning occurs in adults, multiple substances should be suspected.
History is often the most valuable tool. Because many patients (eg, preverbal children, suicidal or psychotic adults, patients with altered consciousness) cannot provide reliable information, friends, relatives, and rescue personnel should be questioned. Even seemingly reliable patients may incorrectly report the amount or time of ingestion. When possible, the patient’s living quarters should be inspected for clues (eg, partially empty pill containers, a suicide note, evidence of recreational drug use). Pharmacy and medical records may provide useful information. In potential workplace poisonings, coworkers and supervisors should be questioned. All industrial chemicals must have a material safety data sheet (MSDS) readily available at the workplace; the MSDS provides detailed information about toxicity and any specific treatment.
In many parts of the world, information about household and industrial chemicals can be obtained from poison control centers. Consultation with the centers is encouraged because ingredients, first-aid measures, and antidotes printed on product containers are occasionally inaccurate or outdated. Also, the container may have been replaced, or the package may have been tampered with. Poison control centers may be able to help identify unknown pills based on their appearance. The centers have ready access to toxicologists. The telephone number of the nearest center is often listed with other emergency numbers in the front of the local telephone book; the number is also available from the telephone operator or, in the US, by dialing 1-800-222-1222. More information is available at the American Association of Poison Control Centers website.
Physical examination sometimes detects signs suggesting particular types of substances (eg, toxidromes [see table Common Toxic Syndromes], breath odor, presence of topical drugs, needle marks or tracks suggesting injected drug use, stigmata of chronic alcohol use).
Even if a patient is known to be poisoned, altered consciousness may be due to other causes (eg, central nervous system infection, head trauma, hypoglycemia, stroke, hepatic encephalopathy, Wernicke encephalopathy), which should also be considered. Attempted suicide must always be considered in older children, adolescents, and adults who have ingested a drug (see Suicidal Behavior and Suicidal Behavior in Children and Adolescents). Also, children often share found pills and substances; careful inquiry to identify additional potentially poisoned patients among playmates and siblings should be undertaken.
Testing
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For most substances, blood levels cannot be easily determined or do not help guide treatment. For a few substances (eg, acetaminophen, aspirin, carbon monoxide, digoxin, ethylene glycol, iron, lithium, methanol, phenobarbital, phenytoin, theophylline), blood levels may help guide treatment. Many authorities recommend measuring acetaminophen levels in all patients with mixed ingestions because acetaminophen ingestion is common, is often asymptomatic during the early stages, and can cause serious delayed toxicity that can be prevented by an antidote. For some substances, other blood tests (eg, PT [prothrombin time] for warfarin overdose, methemoglobin levels for certain substances) help guide treatment.
body packers), plain abdominal x-rays may show the presence and location of ingested substances.
For poisonings with drugs that have cardiovascular effects or with an unknown substance, electrocardiography (ECG) and cardiac monitoring are indicated.
If blood levels of a substance or symptoms of toxicity increase after initially decreasing or persist for an unusually long time, a bezoar, a sustained-release preparation, or reexposure (ie, repeated covert exposure to a recreationally used drug) should be suspected.
Treatment of Poisoning
Supportive care
Occasional use of specific antidotes or dialysis
Only rare use of gastric emptying
Seriously poisoned patients may require assisted ventilation or treatment of cardiovascular collapse. Patients with impaired consciousness may require continuous monitoring or restraints. The discussion of treatment for specific poisonings, below and in tables Common Specific Antidotes, Guidelines for Chelation Therapy, and Symptoms and Treatment of Specific Poisons, is general and does not include specific complexities and details. Consultation with a poison control center is recommended for any poisonings except the mildest and most routine.
Initial stabilization
Maintain airway, breathing, and circulation
IV fluids, sometimes vasopressors
Airway, breathing, and circulation must be maintained in patients suspected of a systemic poisoning. Patients without a pulse or blood pressure require emergency cardiopulmonary resuscitation.
If patients have apnea or compromised airways (eg, foreign material in the oropharynx, decreased gag reflex), an endotracheal tube should be inserted (see Tracheal Intubation). If patients have respiratory depression or hypoxia, supplemental oxygen or mechanical ventilation should be provided as needed.
(2 mg in adults; 0.1 mg/kg in children; doses as high as 10 mg may be necessary in some cases) should be tried in patients with apnea or severe respiratory depression while maintaining airway support. In opioid addicts, naloxone may precipitate withdrawal, but withdrawal is preferable to severe respiratory depression. If respiratory depression persists despite use of naloxone, endotracheal intubation and continuous mechanical ventilation are required. If naloxonenaloxone infusion to maintain respiratory drive without precipitating withdrawal has been suggested but in reality can be very difficult to accomplish.
(50 mL of a 50% solution for adults; 2 to 4 mL/kg of a 25% solution for children) should be given to patients with altered consciousness or central nervous system (CNS) depression, unless hypoglycemia has been ruled out by immediate bedside determination of blood glucose.
IV fluids
Topical decontamination
Any body surface (including the eyes) exposed to a toxin is flushed with large amounts of water or saline. Contaminated clothing, including shoes and socks, and jewelry should be removed. Topical patches and transdermal delivery systems are removed.
Activated charcoal
phenobarbital, theophyllinelithium).
The recommended dose is 5 to 10 times that of the suspected toxin ingested. However, because the amount of toxin ingested is usually unknown, the usual dose is 1 to 2 g/kg, which is about 10 to 25 g for children <
Gastric emptying
Gastric emptying, which used to be well-accepted and seems intuitively beneficial, should not be routinely done. It does not clearly reduce overall morbidity or mortality and has risks. Gastric emptying is considered if it can be done within 1 hour of a life-threatening ingestion. However, many poisonings manifest too late, and whether a poisoning is life threatening is not always clear. Thus, gastric emptying is seldom indicated and, if a caustic substance has been ingested, is contraindicated (see Caustic Ingestion).
For gastric lavage, tap water is instilled and withdrawn from the stomach via a tube. The largest tube possible (usually > 36 French for adults or 24 French for children) is used so that tablet fragments can be retrieved. If patients have altered consciousness or a weak gag reflex, tracheal intubation
Whole-bowel irrigation
This procedure flushes the GI tract and theoretically decreases GI transit time for pills and tablets. Irrigation has not been proved to reduce morbidity or mortality. Irrigation is indicated for any of the following:
A suspected bezoar
Alkaline diuresis
Alkaline diuresis enhances elimination of weak acids (eg, salicylates, phenobarbital> 8, and potassium must be repleted. Hypernatremia, alkalemia, and fluid overload may occur but are usually not serious. However, alkaline diuresis is contraindicated in patients with renal insufficiency.
Dialysis
Common toxins that may require dialysis or hemoperfusion include
Ethylene glycol
Lithium
Methanol
Salicylates
Theophylline
These therapies are less useful if the poison is a large or charged (polar) molecule, has a large volume of distribution (ie, if it is stored in fatty tissue), or is extensively bound to tissue protein (as with digoxin, phencyclidine, phenothiazines, or tricyclic antidepressants). The need for dialysis is usually determined by both laboratory values and clinical status. Methods of dialysis include hemodialysis, peritoneal dialysis, and lipid dialysis (which removes lipid-soluble substances from the blood), as well as hemoperfusion (which more rapidly and efficiently clears specific poisons—see Renal Replacement Therapy).
Specific antidotes
For the most commonly used antidotes, see table Common Specific Antidotes. Chelating drugs are used for poisoning with heavy metals and occasionally with other drugs (see table Guidelines for Chelation Therapy). IV fat emulsions in 10% and 20% concentrations and high-dose insulin therapy have been used to successfully treat several different cardiac toxins (eg, bupivacaine, verapamil).
Ongoing supportive measures
Most symptoms (eg, agitation, sedation, coma, cerebral edema, hypertension, arrhythmias, renal failure, hypoglycemia) are treated with the usual supportive measures (see elsewhere in THE MANUAL).
Hyperthermia is treated with aggressive sedation and physical cooling measures rather than with antipyretics. Organ failure may ultimately require kidney transplantation or liver transplantation.
Hospital admission
General indications for hospital admission include altered consciousness, persistently abnormal vital signs, and predicted delayed toxicity. For example, admission is considered if patients have ingested sustained-release preparations, particularly of drugs with potentially serious effects (eg, cardiovascular drugs). If there are no other reasons for admission, if indicated laboratory test results are normal, and if symptoms are gone after patients have been observed for 4 to 6 hours, most patients can be discharged. However, if ingestion was intentional, patients require a psychiatric evaluation.
Prevention of Poisoning
In the US, widespread use of child-resistant containers with safety caps has greatly reduced the number of poisoning deaths in children < 5 years. Limiting the amount of over-the-counter (OTC) analgesics in a single container and eliminating confusing and redundant formulations reduces the severity of poisonings, particularly with acetaminophen, aspirin, or ibuprofen.
Other preventive measures include
Clearly labeling household products and prescription drugs
Storing drugs and toxic substances in cabinets that are locked and inaccessible to children
Promptly disposing of expired drugs by mixing them in cat litter or some other nontempting substance and putting them in a trash container that is inaccessible to children
Using carbon monoxide detectors
Refraining from prescribing opioids and using nonopioid treatments whenever possible
Public education measures to encourage storage of substances in their original containers (eg, not placing insecticides in drink bottles) are important. Use of imprint identifications on solid drugs helps prevent confusion and errors by patients, pharmacists, and health care practitioners.
Key Points
Poisoning is distinguished from hypersensitivity and idiosyncratic reactions, which are unpredictable and not dose-related, and from intolerance, which is a toxic reaction to a usually nontoxic dose of a substance.
Recognizing a toxidrome (eg, anticholinergic, muscarinic cholinergic, nicotinic cholinergic, opioid, sympathomimetic, withdrawal) can help narrow the differential diagnosis.
Toxicity may be immediate, delayed (eg, acetaminophen, iron, Amanita phalloides mushrooms causing delayed hepatotoxicity), or occur only after repeated exposure.
Maximize recognition of poisoning and identification of the specific poison by considering poisoning in all patients with unexplained alterations in consciousness and by searching thoroughly for clues from the history.
Consider other causes (eg, central nervous system infection, head trauma, hypoglycemia, stroke, hepatic encephalopathy, Wernicke encephalopathy) if consciousness is altered, even if poisoning is suspected.
Use toxicology testing (eg, drug immunoassays) selectively because it can provide incomplete or incorrect information.
More Information
The following is an English-language resource that may be useful. Please note that THE MANUAL is not responsible for the content of this resource.
Hazardous Materials Tools: A searchable database of known toxic substances curated by the U.S. Library of Medicine's Wireless Information System for Emergency Responders (WISER)
