Merck Manual

Please confirm that you are a health care professional

honeypot link

General Principles of Poisoning

By

Gerald F. O’Malley

, DO, Grand Strand Regional Medical Center;


Rika O’Malley

, MD, Albert Einstein Medical Center

Last full review/revision Apr 2020| Content last modified Apr 2020
Click here for Patient Education
Topic Resources

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 table Substances Usually Not Dangerous When Ingested Substances Usually Not Dangerous When Ingested*† 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... read more ); however, almost any substance can be toxic if ingested in excessive amounts.

Table
icon

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 Alcohol Toxicity and Withdrawal Alcohol (ethanol) is a central nervous system depressant. Large amounts consumed rapidly can cause respiratory depression, coma, and death. Large amounts chronically consumed damage the liver... read more , acetaminophen Acetaminophen Poisoning Acetaminophen poisoning can cause gastroenteritis within hours and hepatotoxicity 1 to 3 days after ingestion. Severity of hepatotoxicity after a single acute overdose is predicted by serum... read more , and other over-the-counter (OTC) drugs, may be involved. Accidental poisoning may occur in the elderly 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 Drug-Related Problems in Older Adults Drug-related problems are common in older adults and include drug ineffectiveness, adverse drug effects, overdosage, underdosage, inappropriate treatment, inadequate monitoring, nonadherence... read more ).

After exposure or ingestion and absorption, most poisons are metabolized, pass through the gastrointestinal tract (GI) tract, or are excreted. Occasionally, tablets (eg, aspirin, iron, enteric-coated drugs) form large concretions (bezoars Bezoars A bezoar is a tightly packed collection of partially digested or undigested material that most commonly occurs in the stomach. Gastric bezoars can occur in all age groups and often occur in... read more 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 Symptoms and Treatment of Specific Poisons Symptoms and treatment of specific poisons vary (see table Symptoms and Treatment of Specific Poisons ). Including all the specific complexities and details is impossible, although cross-references... read more ). 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 Common Toxic Syndromes 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... read more ). Patients who ingest multiple substances are less likely to have symptoms characteristic of a single substance.

Table
icon

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.

Some substances (eg, cocaine, phencyclidine, amphetamine) can cause severe agitation, which can result in hyperthermia, acidosis, and rhabdomyolysis.

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 web site.

Physical examination sometimes detects signs suggesting particular types of substances (eg, toxidromes [see table Common Toxic Syndromes Common Toxic Syndromes 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... read more ], 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 Suicidal Behavior Suicide is death caused by an intentional act of self-harm that is designed to be lethal. Suicidal behavior encompasses a spectrum of behavior from suicide attempt and preparatory behaviors... read more and Suicidal Behavior in Children and Adolescents Suicidal Behavior in Children and Adolescents Suicidal behavior includes completed suicide, attempted suicide (with at least some intent to die), and suicide gestures; suicidal ideation is thoughts and plans about suicide. Psychiatric referral... read more ). Also, children often share found pills and substances; careful inquiry to identify additional potentially poisoned patients among playmates and siblings should be undertaken.

Testing

In most cases, laboratory testing provides limited help. Standard, readily available tests to identify common drugs of abuse (often called toxic screens) are qualitative, not quantitative. These tests may provide false-positive or false-negative results, and they check for only a limited number of substances. Also, the presence of a drug of abuse does not necessarily indicate that the drug caused the patient’s symptoms or signs (ie, a patient who had recently taken an opioid may in fact be obtunded because of encephalitis rather than the drug). Urine drug screening is used most often but has limited value and usually detects classes of drugs or metabolites rather than specific drugs. For example, an opioid urine immunoassay test does not detect fentanyl or methadone but does react with very small amounts of morphine or codeine analogues. The test used to identify cocaine detects a metabolite rather than cocaine itself.

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. For patients who have altered consciousness or abnormal vital signs or who have ingested certain substances, tests should include serum electrolytes, blood urea nitrogen (BUN), creatinine, serum osmolality, glucose, coagulation studies, and arterial blood gases (ABGs). Other tests (eg, methemoglobin level, carbon monoxide level, brain CT) may be indicated for certain suspected poisons or in certain clinical situations.

For certain poisonings (eg, due to iron, lead, arsenic, other metals, or to packets of cocaine or other illicit drugs ingested by so-called body packers Body Packing and Body Stuffing Body packing and body stuffing involve swallowing drug-filled packets or placing them in body cavities to evade detection by law enforcement. The risks and consequences vary depending on the... read more ), 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, electroencephalography (EEG) 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 Bezoars A bezoar is a tightly packed collection of partially digested or undigested material that most commonly occurs in the stomach. Gastric bezoars can occur in all age groups and often occur in... read more Bezoars , a sustained-release preparation, or reexposure (ie, repeated covert exposure to a recreationally used drug) should be suspected.

Treatment of Poisoning

  • Supportive care

  • Activated charcoal for serious oral poisonings

  • Occasional use of specific antidotes or dialysis

  • Only rare use of gastric emptying

Initial stabilization

  • Maintain airway, breathing, and circulation

  • IV naloxone

  • IV dextrose and thiamine

  • IV fluids, sometimes vasopressors

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 Tracheal Intubation Most patients requiring an artificial airway can be managed with tracheal intubation, which can be Orotracheal (tube inserted through the mouth) Nasotracheal (tube inserted through the nose)... read more ). If patients have respiratory depression or hypoxia, supplemental oxygen or mechanical ventilation should be provided as needed.

IV naloxone (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 naloxone relieves respiratory depression, patients are monitored; if respiratory depression recurs, patients should be treated with another bolus of IV naloxone or endotracheal intubation and mechanical ventilation. Using a low-dose continuous naloxone infusion to maintain respiratory drive without precipitating withdrawal has been suggested but in reality can be very difficult to accomplish.

IV dextrose (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.

Thiamine (100 mg IV) is given with or before glucose to adults with suspected thiamine deficiency (eg, alcoholics, undernourished patients).

IV fluids are given for hypotension. If fluids are ineffective, invasive hemodynamic monitoring may be necessary to guide fluid and vasopressor therapy. The first-choice vasopressor for most poison-induced hypotension is norepinephrine 0.5 to 1 mg/min IV infusion, but treatment should not be delayed if another vasopressor is more immediately available.

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

Charcoal is usually given, particularly when multiple or unknown substances have been ingested. Use of charcoal adds little risk (unless patients are at risk of vomiting and aspiration) but has not been proved to reduce overall morbidity or mortality. When used, charcoal is given as soon as possible. Activated charcoal adsorbs most toxins because of its molecular configuration and large surface area. Multiple doses of activated charcoal may be effective for substances that undergo enterohepatic recirculation (eg, phenobarbital, theophylline) and for sustained-release preparations. Charcoal may be given at 4- to 6-hour intervals for serious poisoning with such substances unless bowel sounds are hypoactive. Charcoal is ineffective for caustics, alcohols, and simple ions (eg, cyanide, iron, other metals, lithium).

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 < 5 years and 50 to 100 g for older children and adults. Charcoal is given as a slurry in water or soft drinks. It may be unpalatable and results in vomiting in 30% of patients. Administration via a gastric tube may be considered, but caution should be used to prevent trauma caused by tube insertion or aspiration of charcoal; potential benefits must outweigh risks. Activated charcoal should probably be used without sorbitol or other cathartics, which have no clear benefit and can cause dehydration and electrolyte abnormalities.

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 Caustic Ingestion Caustics (strong acids and alkalis), when ingested, burn upper gastrointestinal tract tissues, sometimes resulting in esophageal or gastric perforation. Symptoms may include drooling, dysphagia... read more ).

If gastric emptying is used, gastric lavage is the preferred method. Gastric lavage may cause complications such as epistaxis, aspiration, or, rarely, oropharyngeal or esophageal injury. Syrup of ipecac has unpredictable effects, often causes prolonged vomiting, and may not remove substantial amounts of poison from the stomach. Syrup of ipecac may be warranted if the ingested agent is highly toxic and transport time to the emergency department is unusually long, but this is uncommon in the US.

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 Tracheal Intubation Most patients requiring an artificial airway can be managed with tracheal intubation, which can be Orotracheal (tube inserted through the mouth) Nasotracheal (tube inserted through the nose)... read more should be done before lavage to prevent aspiration. Patients are placed in the left lateral decubitus position to prevent aspiration, and the tube is inserted orally. Because lavage sometimes forces substances farther into the gastrointestinal (GI) tract, stomach contents should be aspirated and a 25-g dose of charcoal should be instilled through the tube immediately after insertion. Then aliquots (about 3 mL/kg) of tap water are instilled, and the gastric contents are withdrawn by gravity or syringe. Lavage continues until the withdrawn fluids appear free of the substance; usually, 500 to 3000 mL of fluid must be instilled. After lavage, a 2nd 25-g dose of charcoal is instilled.

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:

  • Some serious poisonings due to sustained-release preparations or substances that are not adsorbed by charcoal (eg, heavy metals)

  • Drug packets (eg, latex-coated packets of heroin or cocaine ingested by body packers)

  • A suspected bezoar

A commercially prepared solution of polyethylene glycol (which is nonabsorbable) and electrolytes, as sometimes used to cleanse the bowel for colonoscopy, is given at a rate of 1 to 2 L per hour for adults or at 25 to 40 mL/kg/h for children until the rectal effluent is clear; this process may require many hours or even days. The solution is usually given via a gastric tube, although some motivated patients can drink these large volumes.

Alkaline diuresis

Alkaline diuresis enhances elimination of weak acids (eg, salicylates, phenobarbital). A solution made by combining 1 L of 5% D/W with three 50-mEq (50-mmol/L) ampules of sodium bicarbonate and 20 to 40 mEq (20 to 40 mmol/L) of potassium can be given at a rate of 250 mL/h in adults and 2 to 3 mL/kg/h in children. Urine pH is kept at > 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

  • 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 Overview of Renal Replacement Therapy Overview of Renal Replacement Therapy Renal replacement therapy (RRT) replaces nonendocrine kidney function in patients with renal failure and is occasionally used for some forms of poisoning. Techniques include continuous hemofiltration... read more ).

Specific antidotes

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).

Drug-induced hypotension and arrhythmias may not respond to the usual drug treatments. For refractory hypotension, dopamine, epinephrine, other vasopressors, an intra-aortic balloon pump, or even extracorporeal circulatory support may be considered.

For refractory arrhythmias, cardiac pacing may be necessary. Often, torsades de pointes can be treated with magnesium sulfate 2 to 4 g IV, overdrive pacing, or a titrated isoproterenol infusion.

Seizures are first treated with benzodiazepines. Phenobarbital or phenytoin can also be used. Severe agitation must be controlled; benzodiazepines in large doses, other potent sedatives (eg, propofol), or, in extreme cases, induction of paralysis and mechanical ventilation may be required.

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.

  • Treat all poisoning supportively and use activated charcoal for serious oral poisoning and other methods selectively.

More Information

Drugs Mentioned In This Article

Drug Name Select Trade
CALCIUM DISODIUM VERSENATE
NITHIODOTE
No US brand name
THYROSHIELD
CYANOKIT
LEVOPHED
ACETADOTE
PROVAYBLUE
Andexanet Alfa
MESTINON
DILAUDID
CUPRIMINE
TYLENOL
ISUPREL
BUPRENEX
OTREXUP
DESFERAL
ELIXOPHYLLIN
PRAXBIND
VORAXAZE
ISOPTO CARPINE, PILOPINE HS, SALAGEN
XARELTO
PROTOPAM CHLORIDE
BAL
TALWIN
FERRIPROX
TRANSDERM SCOP
EXJADE
ADRENALIN
ADDERALL XR 10
SANDOSTATIN
ANTIZOL
DILANTIN
LANIAZID
OXYCONTIN
DOLOPHINE
ATROPEN
EVZIO
COUMADIN
DURAMORPH PF, MS CONTIN
COMMIT, NICORETTE, NICOTROL
DIPRIVAN
SAVAYSA
ELIQUIS
ACTIQ, DURAGESIC, SUBLIMAZE
CHEMET
LIORESAL
PANHEPRIN
LANOXIN
Click here for Patient Education
NOTE: This is the Professional Version. CONSUMERS: Click here for the Consumer Version
Professionals also read

Test your knowledge

Fractures of the Mandible and Midface
If a patient who sustained blunt trauma to the face has anesthesia in the distribution of the mental nerve, which of the following is the most likely location of the fracture?
Download the Manuals App iOS ANDROID
Download the Manuals App iOS ANDROID
Download the Manuals App iOS ANDROID
Download the Manuals App iOS ANDROID
Download the Manuals App iOS ANDROID
Download the Manuals App iOS ANDROID

Also of Interest

Download the Manuals App iOS ANDROID
Download the Manuals App iOS ANDROID
Download the Manuals App iOS ANDROID
TOP