Harrison’s principles of internal medicine 21st edition 2022 part 14

In addition to the information provided in Table 458-1, severalother aspects of exposure, toxicity, or management are worthy ofdiscussion with respect to the four most hazardous toxicant

PART 14 Poisoning, Drug Overdose, and Envenomation

458 Heavy Metal Poisoning

Howard Hu

Toxic metals (hereafter referred to simply as “metals”) pose a

significant threat to health through low-level as well as high levelenvironmental and occupational exposures One indication of theirimportance relative to other potential hazards is their ranking by theU.S Agency for Toxic Substances and Disease Registry, which

maintains an updated list of all hazards present in toxic waste sitesaccording to their prevalence and the severity of their toxicity Thefirst, second, third, and seventh hazards on the list are heavy metals:arsenic, lead, mercury, and cadmium, respectively

(http://www.atsdr.cdc.gov/spl/) Specific information pertaining toeach of these four metals, including sources and metabolism, toxiceffects produced, diagnosis, and the appropriate treatment for

poisoning, is summarized in Table 458-1

TABLE 458-1 Heavy Metals

Metals are inhaled primarily as dusts and fumes (the latter

defined as tiny particles generated by combustion) Metal poisoningcan also result from exposure to vapors (e.g., mercury vapor in

creating dental amalgams) When metals are ingested in

contaminated food or drink or by hand-to-mouth activity (implicatedespecially in children), their gastrointestinal absorption varies greatlywith the specific chemical form of the metal and the nutritional status

of the host Once a metal is absorbed, blood is the main medium forits transport, with the precise kinetics dependent on diffusibility,

protein binding, rates of biotransformation, availability of intracellularligands, and other factors Some organs (e.g., bone, liver, and

kidney) sequester metals in relatively high concentrations for years.Most metals are excreted through renal clearance and

gastrointestinal excretion; some proportion is also excreted throughsalivation, perspiration, exhalation, lactation, skin exfoliation, and

loss of hair and nails The intrinsic stability of metals facilitates

tracing and measurement in biologic material, although the clinicalsignificance of the levels measured is not always clear

Some metals, such as copper and selenium, are essential tonormal metabolic function as trace elements ( Chap 333 ) but aretoxic at high levels of exposure Others, such as lead and mercury,are xenobiotic and theoretically are capable of exerting toxic effects

at any level of exposure Indeed, much research is currently focused

on the contribution of low-level xenobiotic metal exposure to chronicdiseases and to subtle changes in health that may have significantpublic health consequences Genetic factors, such as

polymorphisms that encode for variant enzymes with altered

properties in terms of metal binding, transport, and effects, also maymodify the impact of metals on health and thereby account, at least

in part, for individual susceptibility to metal effects

The most important component of treatment for metal toxicity is

the termination of exposure Chelating agents are used to bind

metals into stable cyclic compounds with relatively low toxicity and toenhance their excretion The principal chelating agents are

dimercaprol (British anti-Lewisite [BAL]), ethylenediamine tetraaceticacid (EDTA), succimer (dimercaptosuccinic acid [DMSA]), and

penicillamine; their specific use depends on the metal involved andthe clinical circumstances Activated charcoal does not bind metalsand thus is of limited usefulness in cases of acute metal ingestion

In addition to the information provided in Table 458-1, severalother aspects of exposure, toxicity, or management are worthy ofdiscussion with respect to the four most hazardous toxicants

(arsenic, cadmium, lead, and mercury)

Arsenic, even at moderate levels of exposure, has been clearly

linked with increased risks for cancer of the skin, bladder, renal

pelvis, ureter, kidney, liver, and lung These risks appear to be

modified by smoking, folate and selenium status, genetic traits (such

as ability to methylate arsenic), and other factors Recent studies incommunity-based populations have generated strong evidence thatarsenic exposure is also a risk factor for increased risk of

hypertension, coronary heart disease and stroke, lung function

impairment, acute respiratory tract infections, respiratory symptoms,

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and nonmalignant lung disease mortality The association with

cardiovascular disease may hold at levels of exposure in drinkingwater that are below the World Health Organization (WHO)

provisional guideline value of 10 μg/L Evidence has also continued

to build indicating that low-level arsenic is a likely cause of

neurodevelopmental delays in children and likely contributes to thedevelopment of diabetes

Serious cadmium poisoning from the contamination of food and

water by mining effluents in Japan contributed to the 1946 outbreak

of “itai-itai” (“ouch-ouch”) disease, so named because of induced bone toxicity that led to painful bone fractures Modest

cadmium-exposures from environmental contamination have been associated

in some studies with a lower bone density, a higher incidence offractures, and a faster decline in height in both men and women,effects that may be related to cadmium’s calciuric and other toxiceffects on the kidney Cadmium burdens have also been associatedwith an increased risk of long-term kidney graft failure, and there isevidence for synergy between the adverse impacts of cadmium andlead on kidney function Environmental exposures have also beenlinked to lower lung function (even after adjusting for smoking

cigarettes, which contain cadmium) as well as increased risk of

cardiovascular disease and mortality, stroke, and heart failure

Cadmium triggers pulmonary inflammation, and a recent based study of U.S adults found that higher cadmium burdens areassociated with higher mortality from influenza or pneumonia TheInternational Agency for Research on Cancer has classified

population-cadmium as a known carcinogen, with evidence indicating it

contributes to elevated risks of prostate, lung, breast, and

endometrial cancer Overall, this growing body of research indicatesthat cadmium exposure is contributing significantly to morbidity andmortality rates in the general population

Advances in our understanding of lead toxicity have recently

benefited by the development of K x-ray fluorescence (KXRF)

instruments for making safe in vivo measurements of lead levels inbone, which, in turn, reflect cumulative exposure over many years,

as opposed to blood lead levels, which mostly reflect recent

exposure Higher levels of cumulative lead exposure are now known

to be a risk factor for chronic disease, even though blood lead levelshave continued to decline in the general population over the past fewdecades following the removal of lead from gasoline, plumbing,

solder in food cans, and other consumer products, with mean levels

in the U.S population now hovering in the 1–2 μg/dL range For

example, higher bone lead levels measured by KXRF have beenlinked to increased risk of hypertension and accelerated declines incognition in both men and women living in urban communities

These relationships, in conjunction with other epidemiologic andtoxicologic studies, persuaded a federal expert panel to concludethey were causal Prospective studies have also demonstrated thathigher bone lead levels, as well as blood lead levels as low as 1–7μg/dL, are a major risk factor for increased cardiovascular morbidityand mortality rates in both community-based and occupational-

exposed populations Lead exposure at community levels has alsobeen associated with increased risks of hearing loss, Parkinson’sdisease, and amyotrophic lateral sclerosis With respect to

pregnancy-associated risks, high maternal bone lead levels werefound to predict lower birth weight, head circumference, birth length,and neurodevelopmental performance in offspring by age 2 years.Offspring have also been shown to have higher blood pressures atage 7–14 years, an age range at which higher blood pressures areknown to predict an elevated risk of developing hypertension In arandomized trial, calcium supplementation (1200 mg daily) was

found to significantly reduce the mobilization of lead from maternalbone into blood during pregnancy

The toxicity of low-level organic mercury exposure (as manifested

by neurobehavioral performance) is of increasing concern based onstudies of the offspring of mothers who ingested mercury-

contaminated fish With respect to whether the consumption of fish

by women during pregnancy is good or bad for offspring

neurodevelopment, balancing the trade-offs of the beneficial effects

of the omega-3-fatty acids (FAs) in fish versus the adverse effects ofmercury contamination in fish has led to some confusion and

inconsistency in public health recommendations Overall, it wouldappear that it would be best for pregnant women to either limit fishconsumption to those species known to be low in mercury

contamination but high in omega-3-FAs (such as sardines or

mackerel) or to avoid fish and obtain omega-3-FAs through

supplements or other dietary sources Accumulated evidence hasnot supported the contention that ethyl mercury, used as a

preservative in multiuse vaccines administered in early childhood,has played a significant role in causing neurodevelopmental

problems such as autism With regard to adults, there is conflictingevidence as to whether mercury exposure is associated with

increased risk of hypertension and cardiovascular disease There isalso some evidence that mercury exposure in the general population

is associated with the development of diabetes, perturbations in

markers of autoimmunity, and depression At this point, conclusionscannot be drawn and the clinical significance of these findings

remains unclear

Heavy metals pose risks to health that are especially

burdensome in selected parts of the world For example, arsenic

exposure from natural contamination of shallow tube wells insertedfor drinking water is a major environmental problem for millions ofresidents in parts of Bangladesh and Western India Contaminationwas formerly considered only a problem with deep wells; however,the geology of this region allows most residents only a few

alternatives for potable drinking water Arsenic contamination of

drinking water is also a major problem in China, Argentina, Chile,Mexico, and some regions of the United States (Maine, New

Hampshire, Massachusetts) The global campaign to phase out

leaded gasoline has had continued success, with only a few

countries still remaining (Algeria, Iraq, Yemen, Myanmar, North

Korea, and Afghanistan) However, significant population exposures

to lead remain, particularly in the United States with respect to olderhousing that contains lead paint or that receives drinking water

through lead pipes, and there are indications that exposures arebeginning to increase again in many low- and middle-income

countries due to industrial pollution, electronic waste, and a variety ofcontaminated consumer products Populations living in the Arctic

have been shown to have particularly high exposures to mercury due

to long-range transport patterns that concentrate mercury in the

polar regions, as well as the traditional dependence of Arctic peoples

on the consumption of fish and other wildlife that bioconcentratemethylmercury.

A few additional metals deserve brief mention but are not

covered in Table 458-1 because of the relative rarity of their beingclinically encountered or the uncertainty regarding their potential

toxicities Aluminum contributes to the encephalopathy in patients

with severe renal disease, who are undergoing dialysis ( Chap 410 ).High levels of aluminum are found in the neurofibrillary tangles in thecerebral cortex and hippocampus of patients with Alzheimer’s

disease, as well as in the drinking water and soil of areas with anunusually high incidence of Alzheimer’s The experimental and

epidemiologic evidence for the aluminum–Alzheimer’s disease linkremains relatively weak, however, and it cannot be concluded thataluminum is a causal agent or a contributing factor in

neurodegenerative disease Hexavalent chromium is corrosive andsensitizing Workers in the chromate and chrome pigment productionindustries have consistently had a greater risk of lung cancer The

introduction of cobalt chloride as a fortifier in beer led to outbreaks of

fatal cardiomyopathy among heavy consumers Occupational

exposure (e.g., of miners, dry-battery manufacturers, and arc

welders) to manganese (Mn) can cause a parkinsonian syndrome

within 1–2 years, including gait disorders; postural instability; a

masked, expressionless face; tremor; and psychiatric symptoms.With the introduction of methylcyclopentadienyl manganese

tricarbonyl (MMT) as a gasoline additive, there is concern for thetoxic potential of environmental manganese exposure Some

epidemiologic studies have found an association between the

prevalence of parkinsonian disorders and estimated manganeseexposures emitted by local ferroalloy industries; others have foundevidence suggesting that manganese may interfere with early

childhood neurodevelopment in ways similar to that of lead

Manganese toxicity is clearly associated with dopaminergic

dysfunction, and its toxicity is likely influenced by age, gender,

ethnicity, genetics, and preexisting medical conditions Nickel

exposure induces an allergic response, and inhalation of nickel

compounds with low aqueous solubility (e.g., nickel subsulfide andnickel oxide) in occupational settings is associated with an increased

risk of lung cancer Overexposure to selenium may cause local

irritation of the respiratory system and eyes, gastrointestinal irritation,liver inflammation, loss of hair, depigmentation, and peripheral nerve

damage Workers exposed to certain organic forms of tin

(particularly trimethyl and triethyl derivatives) have developed

psychomotor disturbances, including tremor, convulsions,

hallucinations, and psychotic behavior

Thallium, which is a component of some insecticides, metal

alloys, and fireworks, is absorbed through the skin as well as by

ingestion and inhalation Severe poisoning follows a single ingesteddose of >1 g or >8 mg/kg Nausea and vomiting, abdominal pain,and hematemesis precede confusion, psychosis, organic brain

syndrome, and coma Thallium is radiopaque Induced emesis orgastric lavage is indicated within 4–6 h of acute ingestion; Prussianblue prevents absorption and is given orally at 250 mg/kg in divideddoses Unlike other types of metal poisoning, thallium poisoning may

be less severe when activated charcoal is used to interrupt its

enterohepatic circulation Other measures include forced diuresis,treatment with potassium chloride (which promotes renal excretion ofthallium), and peritoneal dialysis

Chelation therapy remains the treatment of choice for most toxic

metals in the setting of severe acute clinical poisoning However, theuse of chelation for treating chronic diseases remains controversial,

in part because of the lack of evidence from rigorous randomizedclinical trials One area for which there is moderate evidence is theuse of chelation in patients with higher than average levels of

accumulated lead burdens as a means of improving kidney function.The results from a series of randomized trials conducted in Taiwansuggest that among individuals with mildly elevated lead burdens(defined as between 150 and 600 μg of lead per 72-h urine upon anEDTA mobilization test [1 g EDTA]), weekly calcium disodium EDTAchelation treatments for between 2 and 27 months can improve renalfunction outcomes, both in individuals with and without type 2

years who had experienced a myocardial infarction (MI), found that aprotocol of repeated intravenous chelation with disodium EDTA,

compared with placebo, modestly but significantly reduced the risk ofadverse cardiovascular outcomes, many of which were

revascularization procedures The effect was particularly pronouncedamong those with concurrent diabetes However, the trial did notinclude rigorous measures of exposure to lead or other metals or anyselection criteria based on metals exposure; thus, even though

chelation reduces metal burdens, which have been associated withadverse cardiovascular effects (especially lead), it remains unclearwhether the beneficial effects result from a reduction in metal

burden In view of the risks of side effects associated with chelation,

by themselves, the results are not sufficient to support the routineuse of chelation therapy for treatment of patients either who havehad an MI or who have had low-level lead exposure A follow-up trialwith rigorous measures of metals exposure is ongoing

therapy Curr Atheroscler Rep 18:81, 2016

GIDLOW DA: Lead toxicity Occup Med (Lond) 65:348, 2015

KIM KH et al: A review on the distribution of Hg in the environmentand its human health impacts J Hazard Mater 306:376, 2016.LAMAS GA et al: Heavy metals, cardiovascular disease, and the

unexpected benefits of chelation therapy J Am Coll Cardiol

67:2411, 2016

LANPHEAR BP et al: Low-level lead exposure and mortality in US

adults: A population-based cohort study Lancet Public Health3:e177, 2018

O’NEAL SL, ZHENG W: Manganese toxicity upon overexposure: Adecade in review Curr Environ Health Rep 2:315, 2015

PARK SK et al: Environmental cadmium and mortality from influenzaand pneumonia in U.S adults Environ Health Perspect

128:127004, 2020

TELLEZ-PLAZA M et al: Cadmium exposure and all-cause and

cardiovascular mortality in the U.S general population EnvironHealth Perspect 120:1017, 2012

WEAVER VM et al: Does calcium disodium EDTA slow CKD

progression? Am J Kidney Dis 60:503, 2012

XU L et al: Positive association of cardiovascular disease (CVD) withchronic exposure to drinking water arsenic (As) at concentrationsbelow the WHO provisional guideline value: A systematic reviewand meta-analysis Int J Environ Res Public Health 17:2536,2020

459 Poisoning and Drug Overdose

to a given dose may vary because of genetic polymorphism,

enzymatic induction or inhibition in the presence of other xenobiotics,

or acquired tolerance Poisoning may be local (e.g., skin, eyes, orlungs) or systemic depending on the route of exposure, the chemicaland physical properties of the poison, and its mechanism of action.The severity and reversibility of poisoning also depend on the

functional reserve of the individual or target organ, which is

influenced by age and preexisting disease

EPIDEMIOLOGY

More than 5 million poison exposures occur in the United Stateseach year Most are acute, are accidental (unintentional), involve asingle agent, occur in the home (>90%), result in minor or no toxicity,and involve children <6 years of age Pharmaceuticals are involved

in 47% of poisoning exposures and in 84% of serious or fatal

poisonings Household cleaning substances and cosmetics/personalcare products are the most common nonpharmaceutical exposuresreported to the National Poison Data System (NPDS) In the lastdecade, the rate of injury-related deaths from poisoning has

overtaken the rate of deaths related to motor-vehicle crashes in theUnited States According to the Centers for Disease Control andPrevention (CDC), twice as many Americans died from drug

overdoses in 2014 compared to 2000 Although prescription opioidshave appropriately received attention as a major reason for the

increased number of poisoning deaths, the availability of other

pharmaceuticals and rapid proliferation of novel drugs of abuse also

contribute to the increasing death rate In many parts of the UnitedStates, where these issues are particularly prevalent, there are

efforts to develop better prescription drug databases and enhancedtraining for health care professionals in pain management and theuse of opioids Unintentional exposures can result from the improperuse of chemicals at work or play; label misreading; product

mislabeling; mistaken identification of unlabeled chemicals;

uninformed self-medication; and dosing errors by nurses,

pharmacists, physicians, parents, and the elderly Excluding the

recreational use of ethanol, attempted suicide (deliberate self-harm)

is the most common reported reason for intentional poisoning

Recreational use of prescribed and over-the-counter drugs for

psychotropic or euphoric effects (abuse) or excessive self-dosing (misuse) is increasingly common and may also result in unintentional

self-poisoning

About 20–25% of exposures require bedside health-professionalevaluation, and 5% of all exposures require hospitalization

Poisonings account for 5–10% of all ambulance transports,

emergency department visits, and intensive care unit admissions.Hospital admissions related to poisoning are also associated withlonger lengths of stay and increase the utilization of resources such

as radiography and other laboratory services Up to 35% of

psychiatric admissions are prompted by attempted suicide via

overdosage with cases involving adolescents steadily increasingduring the last decade Overall, the mortality rate is low: <1% of allpoisoning exposures It is significantly higher (1–2%) among

hospitalized patients with intentional (suicidal) overdose or

complications from drugs of abuse, who account for the majority ofserious poisonings Acetaminophen is the pharmaceutical agentmost often implicated in fatal poisoning Overall, carbon monoxide isthe leading cause of death from poisoning, but this prominence is notreflected in hospital or poison center statistics because patients withsuch poisoning are typically dead when discovered and are referreddirectly to medical examiners

DIAGNOSIS

Although poisoning can mimic other illnesses, the correct diagnosiscan usually be established by the history, physical examination,

routine and toxicologic laboratory evaluations, and characteristicclinical course

■ HISTORY

The history should include the time, route, duration, and

circumstances (location, surrounding events, and intent) of

exposure; the name and amount of each drug, chemical, or

ingredient involved; the time of onset, nature, and severity of

symptoms; the time and type of first-aid measures provided; the

medical and psychiatric history; and occupation

In many cases, the patient is confused, comatose, unaware of anexposure, or unable or unwilling to admit to one Suspicious

circumstances include unexplained sudden illness in a previouslyhealthy person or a group of healthy people; a history of psychiatricproblems (particularly depression or bipolar disorder); recent

changes in health, economic status, or social relationships; and

onset of illness during work with chemicals or after ingestion of food,drink (especially ethanol), or medications When patients become illsoon after arriving from a foreign country or being arrested for

criminal activity, “body packing” or “body stuffing” (ingesting or

concealing illicit drugs in a body cavity) should be suspected

Relevant information may be available from family, friends,

paramedics, police, pharmacists, physicians, and employers, whoshould be questioned regarding the patient’s habits, hobbies,

behavioral changes, available medications, and antecedent events.Patients need to be asked explicitly about their prescribed

medications and recreational drug use Drugs previously considered

“illicit” such as cannabinoids are now legal in many states and

prescribed for therapeutic purposes A search of clothes, belongings,and place of discovery may reveal a suicide note or a container ofdrugs or chemicals Without a clear history in a patient clinically

suspected to be poisoned, all medications available anywhere in thepatient’s home or belongings should be considered as possible

agents, including medications for pets Review of the patient’s record

in the state prescription monitoring program (PMP) may disclose

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relevant history of Schedule II, III, IV, and V controlled substanceuse The imprint code on pills and the label on chemical productsmay be used to identify the ingredients and potential toxicity of asuspected poison by consulting a reference text, a computerizeddatabase, the manufacturer, or a regional poison information center(800-222-1222) Occupational exposures require review of any

available safety data sheet (SDS) from the worksite Because ofincreasing globalization from travel and internet consumerism,

unfamiliar poisonings may result in local emergency department

evaluation Pharmaceuticals, industrial chemicals, or drugs of abusefrom foreign countries may be identified with the assistance of a

regional poison center or via the World Wide Web

The physical examination should focus initially on vital signs, the

cardiopulmonary system, and neurologic status The neurologic

examination should include documentation of neuromuscular

abnormalities such as dyskinesia, dystonia, fasciculations,

myoclonus, rigidity, and tremors The patient should also be

examined for evidence of trauma and underlying illnesses Focalneurologic findings are uncommon in poisoning, and their presenceshould prompt evaluation for a structural central nervous system(CNS) lesion Examination of the eyes (for nystagmus and pupil sizeand reactivity), abdomen (for bowel activity and bladder size), andskin (for burns, bullae, color, warmth, moisture, pressure sores, andpuncture marks) may reveal findings of diagnostic value When thehistory is unclear, all orifices should be examined for the presence ofchemical burns and drug packets The odor of breath or vomitus andthe color of nails, skin, or urine may provide important diagnosticclues

The diagnosis of poisoning in cases of unknown etiology primarilyrelies on pattern recognition The first step is to assess the pulse,blood pressure, respiratory rate, temperature, and neurologic statusand to characterize the overall physiologic state as stimulated,

depressed, discordant, or normal ( Table 459-1 ) Obtaining a

complete set of vital signs and reassessing them frequently are

critical Measuring core temperature is especially important, even in

difficult or combative patients, since temperature elevation is themost reliable prognosticator of poor outcome in poisoning from

stimulants (e.g., cocaine) or drug withdrawal (e.g., alcohol or

γ-hydroxybutyric acid [GHB]) The next step is to consider the

underlying causes of the physiologic state and to attempt to identify

a pathophysiologic pattern or toxic syndrome (toxidrome) based on

the observed findings Assessing the severity of physiologic

derangements ( Table 459-2 ) is useful in this regard and also for

monitoring the clinical course and response to treatment In cases ofpolydrug overdose involving different drug classes, identifying a cleartoxidrome can be challenging if the different drugs counteract thephysiologic effects of one another The final step is to attempt to

identify the particular agent involved by looking for unique or

relatively poison-specific physical or ancillary test abnormalities

Distinguishing among toxidromes on the basis of the physiologicstate is summarized next

TABLE 459-1 Differential Diagnosis of Poisoning Based on

Physiologic State

The Stimulated Physiologic State Increased pulse, blood

pressure, respiratory rate, temperature, and neuromuscular activity

characterize the stimulated physiologic state, which can reflect

sympathetic, anticholinergic, or hallucinogen poisoning or drug

withdrawal (Table 459-1) Other features are noted in Table 459-2.Mydriasis, a characteristic feature of all stimulants, is most marked inanticholinergic poisoning since pupillary reactivity relies on

muscarinic control In sympathetic poisoning (e.g., due to cocaine),pupils are also enlarged, but some reactivity to light remains The

anticholinergic toxidrome is also distinguished by hot, dry, flushedskin; decreased bowel sounds; and urinary retention Other stimulantsyndromes increase sympathetic activity and cause diaphoresis,pallor, and increased bowel activity with varying degrees of nausea,vomiting, abnormal distress, and occasionally diarrhea The absoluteand relative degree of vital-sign changes and neuromuscular

hyperactivity can help distinguish among stimulant toxidromes Sincesympathetics stimulate the peripheral nervous system more directlythan do hallucinogens or drug withdrawal, markedly increased vitalsigns and organ ischemia suggest sympathetic poisoning Findingshelpful in suggesting the particular drug or class causing physiologicstimulation include reflex bradycardia from selective α-adrenergicstimulants (e.g., decongestants), hypotension from selective β-

adrenergic stimulants (e.g., asthma therapeutics), limb ischemiafrom ergot alkaloids, rotatory nystagmus from phencyclidine andketamine (the only physiologic stimulants that cause this finding),and delayed cardiac conduction from high doses of cocaine andsome anticholinergic agents (e.g., antihistamines, cyclic

antidepressants, and antipsychotics) Seizures suggest a

sympathetic etiology, an anticholinergic agent with membrane-activeproperties (e.g., cyclic antidepressants, phenothiazines), or a

withdrawal syndrome Close attention to core temperature is critical

in patients with grade 4 physiologic stimulation (Table 459-2)

TABLE 459-2 Severity of Physiologic Stimulation and

Depression in Poisoning and Drug Withdrawal

The Depressed Physiologic State Decreased pulse, blood

pressure, respiratory rate, temperature, and neuromuscular activity

are indicative of the depressed physiologic state caused by

“functional” sympatholytics (agents that decrease cardiac functionand vascular tone as well as sympathetic activity), cholinergic

(muscarinic and nicotinic) agents, opioids, and sedative-hypnotic aminobutyric acid (GABA)-ergic agents (Tables 459-1 and 459-2).Miosis is also common and is most pronounced in opioid and

γ-cholinergic poisoning Miosis is distinguished from other depressantsyndromes by muscarinic and nicotinic signs and symptoms (Table459-1) Pronounced cardiovascular depression in the absence ofsignificant CNS depression suggests a direct or peripherally actingsympatholytic In contrast, in opioid and sedative-hypnotic poisoning,vital-sign changes are secondary to depression of CNS

cardiovascular and respiratory centers (or consequent hypoxemia),

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and significant abnormalities in these parameters do not occur untilthere is a marked decrease in the level of consciousness (grade 3 or

4 physiologic depression; Table 459-2) Other clues that suggest thecause of physiologic depression include cardiac arrhythmias andconduction disturbances (due to antiarrhythmics, β-adrenergic

antagonists, calcium channel blockers, digitalis glycosides,

propoxyphene, and cyclic antidepressants), mydriasis (due to

tricyclic antidepressants, some antiarrhythmics, meperidine, anddiphenoxylate-atropine [Lomotil]), nystagmus (due to sedative-

hypnotics), and seizures (due to cholinergic agents, propoxyphene,and cyclic antidepressants)

The Discordant Physiologic State The discordant physiologic state

is characterized by mixed vital-sign and neuromuscular

abnormalities, as observed in poisoning by asphyxiants, CNS

syndromes, membrane-active agents, and anion-gap metabolic

acidosis (AGMA) inducers (Table 459-1) In these conditions,

manifestations of physiologic stimulation and physiologic depressionoccur together or at different times during the clinical course Forexample, membrane-active agents can cause simultaneous coma,seizures, hypotension, and tachyarrhythmias Alternatively, vital

signs may be normal while the patient has an altered mental status

or is obviously sick or clearly symptomatic Early, pronounced sign and mental-status changes suggest asphyxiant or membrane-active agent poisoning; the lack of such abnormalities suggests anAGMA inducer; and marked neuromuscular dysfunction without

vital-significant vital-sign abnormalities suggests a CNS syndrome The

discordant physiologic state may also be evident in patients

poisoned with multiple agents

The Normal Physiologic State A normal physiologic status and

physical examination may be due to a nontoxic exposure,

psychogenic illness, or poisoning by “toxic time-bombs”: agents thatare slowly absorbed, are slowly distributed to their sites of action,require metabolic activation, or disrupt metabolic processes (Table459-1) Because so many medications have now been reformulatedinto once-a-day preparations for the patient’s convenience and

adherence, toxic time-bombs are increasingly common Diagnosing

a nontoxic exposure requires that the identity of the exposure agent

be known or that a toxic time-bomb exposure be excluded and thetime since exposure exceed the longest known or predicted intervalbetween exposure and peak toxicity Psychogenic illness (fear ofbeing poisoned, mass hysteria) may also follow a nontoxic exposureand should be considered when symptoms are inconsistent withexposure history Anxiety reactions resulting from a nontoxic

exposure can cause mild physiologic stimulation (Table 459-2) and

be indistinguishable from toxicologic causes without ancillary testing

or a suitable period of observation

Laboratory assessment may be helpful in the differential diagnosis.

Increased AGMA is most common in advanced methanol, ethyleneglycol, and salicylate intoxication but can occur with any poisoningthat results in hepatic, renal, or respiratory failure; seizures; or

shock The serum lactate concentration is more commonly low (lessthan the anion gap) in the former and high (nearly equal to the aniongap) in the latter An abnormally low anion gap can be due to

elevated blood levels of bromide, calcium, iodine, lithium, or

magnesium An increased osmolal gap—a difference of >10 mmol/Lbetween serum osmolality (measured by freezing-point depression)and osmolality calculated from serum sodium, glucose, and bloodurea nitrogen levels—suggests the presence of a low-molecular-weight solute such as acetone; an alcohol (benzyl, ethanol,

isopropanol, methanol); a glycol (diethylene, ethylene, propylene);ether (ethyl, glycol); or an “unmeasured” cation (calcium,

magnesium) or sugar (glycerol, mannitol, sorbitol) Ketosis suggestsacetone, isopropyl alcohol, salicylate poisoning, or alcoholic

ketoacidosis Hypoglycemia may be due to poisoning with

β-adrenergic blockers, ethanol, insulin, oral hypoglycemic agents,quinine, and salicylates, whereas hyperglycemia can occur in

poisoning with acetone, β-adrenergic agonists, caffeine, calcium

channel blockers, iron, theophylline, or

N-3-pyridylmethyl-N′-p-nitrophenylurea (PNU [Vacor]) Hypokalemia can be caused by

barium, β-adrenergic agonists, caffeine, diuretics, theophylline, or

toluene; hyperkalemia suggests poisoning with an α-adrenergic

agonist, a β-adrenergic blocker, cardiac glycosides, or fluoride

Hypocalcemia may be seen in ethylene glycol, fluoride, and oxalatepoisoning Prothrombin time and international normalized ratio areuseful for risk stratification in cases of warfarin or rodenticide

poisoning but are not to be relied on when evaluating overdose orcomplications from novel oral anticoagulant pharmaceuticals (directthrombin inhibitors and direct factor Xa inhibitors)

The electrocardiogram (ECG) can be useful for rapid diagnostic

purposes Bradycardia and atrioventricular block may occur in

patients poisoned by α-adrenergic agonists, antiarrhythmic agents,beta blockers, calcium channel blockers, cholinergic agents

(carbamate and organophosphate insecticides), cardiac glycosides,lithium, or tricyclic antidepressants QRS- and QT-interval

prolongation may be caused by hyperkalemia, various

antidepressants, and other membrane-active drugs (Table 459-1).Ventricular tachyarrhythmias may be seen in poisoning with cardiacglycosides, fluorides, membrane-active drugs, methylxanthines,

sympathomimetics, antidepressants, and agents that cause

hyperkalemia or potentiate the effects of endogenous

catecholamines (e.g., chloral hydrate, aliphatic and halogenatedhydrocarbons)

Radiologic studies may occasionally be useful Pulmonary edema

(adult respiratory distress syndrome [ARDS]) can be caused by

poisoning with carbon monoxide, cyanide, an opioid, paraquat,

phencyclidine, a sedative-hypnotic, or salicylate; by inhalation ofirritant gases, fumes, or vapors (acids and alkali, ammonia,

aldehydes, chlorine, hydrogen sulfide, isocyanates, metal oxides,mercury, phosgene, polymers); or by prolonged anoxia,

hyperthermia, or shock Aspiration pneumonia is common in patientswith coma, seizures, and petroleum distillate aspiration Chest x-ray

is useful for identifying complications from metal fume fever or

elemental mercury The presence of radiopaque densities on

abdominal x-rays or abdominal computed tomography (CT) scansuggests the ingestion of chloral hydrate, chlorinated hydrocarbons,heavy metals, illicit drug packets, iodinated compounds, potassiumsalts, enteric-coated tablets, or salicylates

Toxicologic analysis of urine and blood (and occasionally of

gastric contents and chemical samples) can sometimes confirm orrule out suspected poisoning Interpretation of laboratory data

requires knowledge of the qualitative and quantitative tests used forscreening and confirmation (enzyme-multiplied, fluorescence

polarization, and radio-immunoassays; colorimetric and fluorometricassays; thin-layer, gas-liquid, or high-performance liquid

chromatography; gas chromatography; mass spectrometry), theirsensitivity (limit of detection) and specificity, the preferred biologicspecimen for analysis, and the optimal time of specimen sampling.Personal communication with the hospital laboratory is essential to

an understanding of institutional testing capabilities and limitations

Rapid qualitative hospital-based urine tests for drugs of abuse

are only screening tests that cannot confirm the exact identity of thedetected substance and should not be considered diagnostic or usedfor forensic purposes False-positive and false-negative results arecommon A positive screen may result from other pharmaceuticalsthat interfere with laboratory analysis (e.g., fluoroquinolones

commonly cause false-positive opiate screens) Confirmatory testingwith gas chromatography/mass spectrometry can be requested, but

it often takes weeks to obtain a reported result A negative screeningresult may mean that the responsible substance is not detectable bythe test used or that its concentration is too low for detection at thetime of sampling For instance, recent new drugs of abuse that oftenresult in emergency department evaluation for unexpected

complications, such as synthetic cannabinoids (spice), cathinones(bath salts), and opiate substitutes (kratom), are not detectable byhospital-based tests In cases where a drug concentration is too low

to be detected early during clinical evaluation, repeating the test at alater time may yield a positive result Patients symptomatic from

drugs of abuse often require immediate management based on thehistory, physical examination, and observed toxidrome without

laboratory confirmation (e.g., apnea from opioid intoxication) Whenthe patient is asymptomatic or when the clinical picture is consistentwith the reported history, qualitative screening is neither clinicallyuseful nor cost-effective Thus, qualitative drug screens are of

greatest value for the evaluation of patients with severe or

unexplained toxicities, such as coma, seizures, cardiovascular

instability, metabolic or respiratory acidosis, and nonsinus cardiac

rhythms In contrast to qualitative drug screens, quantitative serum

tests are useful for evaluation of patients poisoned with

acetaminophen ( Chap 340 ), alcohols (including ethylene glycol andmethanol), anticonvulsants, barbiturates, digoxin, heavy metals, iron,lithium, salicylate, and theophylline, as well as for the presence ofcarboxyhemoglobin and methemoglobin The serum concentration inthese cases guides clinical management, and results are often

available within an hour

The response to antidotes is sometimes useful for diagnostic

purposes Resolution of altered mental status and abnormal vitalsigns within minutes of IV administration of dextrose, naloxone, orflumazenil is virtually diagnostic of hypoglycemia, opioid poisoning,and benzodiazepine intoxication, respectively The prompt reversal

of dystonic (extrapyramidal) signs and symptoms following an IVdose of benztropine or diphenhydramine confirms a drug etiology.Although complete reversal of both central and peripheral

manifestations of anticholinergic poisoning by physostigmine is

diagnostic of this condition, physostigmine may cause some arousal

in patients with CNS depression of any etiology

TABLE 459-3 Fundamentals of Poisoning Management

During the pretoxic phase, prior to the onset of poisoning,

decontamination is the highest priority, and treatment is basedsolely on the history The maximal potential toxicity based on thegreatest possible exposure should be assumed Since

decontamination is more effective when accomplished soon afterexposure and when the patient is asymptomatic, the initial historyand physical examination should be focused and brief It is also

advisable to establish IV access and initiate cardiac monitoring,particularly in patients with potentially serious ingestions or unclearhistories.

When an accurate history is not obtainable and a poison causingdelayed toxicity (i.e., a toxic time-bomb) or irreversible damage issuspected, blood and urine should be sent for appropriate

toxicologic screening and quantitative analysis During poison

absorption and distribution, blood levels may be greater than those

in tissue and may not correlate with toxicity However, high bloodlevels of agents whose metabolites are more toxic than the parentcompound (acetaminophen, ethylene glycol, or methanol) may

indicate the need for additional interventions (antidotes, dialysis).Most patients who remain asymptomatic or who become

asymptomatic 6 h after ingestion are unlikely to develop subsequenttoxicity and can be discharged safely Longer observation will benecessary for patients who have ingested toxic time-bombs

During the toxic phase—the interval between the onset of

poisoning and its peak effects—management is based primarily on

clinical and laboratory findings Effects after an overdose usually begin sooner, peak later, and last longer than they do after a

therapeutic dose A drug’s published pharmacokinetic profile in

standard references such as the Physician’s Desk Reference (PDR)

is usually different from its toxicokinetic profile in overdose

Resuscitation and stabilization are the first priority Symptomaticpatients should have an IV line placed and should undergo oxygensaturation determination, cardiac monitoring, and continuous

observation Baseline laboratory, ECG, and x-ray evaluation mayalso be appropriate Intravenous glucose (unless the serum level isdocumented to be normal), naloxone, and thiamine should be

considered in patients with altered mental status, particularly thosewith coma or seizures Decontamination should also be considered,but it is less likely to be effective during this phase than during thepretoxic phase

Measures that enhance poison elimination may shorten the

duration and severity of the toxic phase However, they are not

without risk, which must be weighed against the potential benefit.Diagnostic certainty (usually via laboratory confirmation) is generally

a prerequisite Intestinal (gut) dialysis with repetitive doses of

activated charcoal (see “Multiple-Dose Activated Charcoal,” later)can enhance the elimination of selected poisons such as

theophylline or carbamazepine Urinary alkalinization may enhancethe elimination of salicylates and a few other poisons Chelationtherapy can enhance the elimination of selected metals

Extracorporeal elimination methods are effective for many poisons,but their expense and risk make their use reasonable only in

patients who would otherwise have an unfavorable outcome

During the resolution phase of poisoning, supportive care and

monitoring should continue until clinical, laboratory, and ECG

abnormalities have resolved Since chemicals are eliminated soonerfrom the blood than from tissues, blood levels are usually lower thantissue levels during this phase and again may not correlate withtoxicity This discrepancy applies particularly when extracorporealelimination procedures are used Redistribution from tissues maycause a rebound increase in the blood level after termination ofthese procedures (e.g., lithium) When a metabolite is responsiblefor toxic effects, continued treatment may be necessary in the

absence of clinical toxicity or abnormal laboratory studies

SUPPORTIVE CARE

The goal of supportive therapy is to maintain physiologic

homeostasis until detoxification is accomplished and to prevent andtreat secondary complications such as aspiration, bedsores,

cerebral and pulmonary edema, pneumonia, rhabdomyolysis, renalfailure, sepsis, thromboembolic disease, coagulopathy, and

generalized organ dysfunction due to hypoxemia or shock

Admission to an intensive care unit is indicated for the following:patients with severe poisoning (coma, respiratory depression,

hypotension, cardiac conduction abnormalities, cardiac arrhythmias,hypothermia or hyperthermia, seizures); those needing close

monitoring, antidotes, or enhanced elimination therapy; those

showing progressive clinical deterioration; and those with significantunderlying medical problems Patients with mild to moderate toxicitycan be managed on a general medical service, on an intermediatecare unit, or in an emergency department observation area,

depending on the anticipated duration and level of monitoring

needed (intermittent clinical observation vs continuous clinical,

cardiac, and respiratory monitoring) Patients who have attemptedsuicide require continuous observation and measures to preventself-injury until they are no longer suicidal

Respiratory Care Endotracheal intubation for protection againstthe aspiration of gastrointestinal contents is of paramount

importance in patients with CNS depression or seizures as thiscomplication can increase morbidity and mortality rates Mechanicalventilation may be necessary for patients with respiratory

depression or hypoxemia and for facilitation of therapeutic sedation

or paralysis of patients in order to prevent or treat hyperthermia,acidosis, and rhabdomyolysis associated with neuromuscular

hyperactivity Since clinical assessment of respiratory function can

be inaccurate, the need for oxygenation and ventilation is best

determined by continuous pulse oximetry or arterial blood-gas

analysis The gag reflex is not a reliable indicator of the need forintubation A patient with CNS depression may maintain airwaypatency while being stimulated but not if left alone Drug-inducedpulmonary edema is usually noncardiac rather than cardiac in

origin, although profound CNS depression and cardiac conductionabnormalities suggest the latter Measurement of pulmonary arterypressure may be necessary to establish the cause and direct

appropriate therapy Extracorporeal measures (membrane

oxygenation, extracorporeal membrane oxygenation [ECMO],

venoarterial perfusion, cardiopulmonary bypass) and partial liquid(perfluorocarbon) ventilation may be appropriate for severe butreversible respiratory failure In the last decade, ECMO has beenincreasingly used for critically ill poisoned patients where standardresuscitative therapy or antidotes have not been helpful, but furtherresearch is still needed to determine the right toxicologic indicationsfor this treatment strategy

Cardiovascular Therapy Maintenance of normal tissue perfusion

is critical for complete recovery to occur once the offending agenthas been eliminated Focused bedside echocardiography or

measurement of central venous pressure may help prioritize

therapeutic strategies If hypotension is unresponsive to volume

expansion and appropriate goal-directed antidotal therapy,

treatment with norepinephrine, epinephrine, or high-dose dopaminemay be necessary Intraaortic balloon pump counterpulsation andvenoarterial or cardiopulmonary perfusion techniques should beconsidered for severe but reversible cardiac failure For patientswith a return of spontaneous circulation after resuscitative treatmentfor cardiopulmonary arrest secondary to poisoning, therapeutic

hypothermia should be used according to protocol

Bradyarrhythmias associated with hypotension generally should betreated as described in Chaps 244 and 245 Glucagon, calcium,and high-dose insulin with dextrose may be effective in beta blockerand calcium channel blocker poisoning Antibody therapy may beindicated for cardiac glycoside poisoning

Supraventricular tachycardia associated with hypertension andCNS excitation is almost always due to agents that cause

generalized physiologic excitation (Table 459–1) Most cases aremild or moderate in severity and require only observation or

nonspecific sedation with a benzodiazepine In severe cases orthose associated with hemodynamic instability, chest pain, or ECGevidence of ischemia, specific therapy is indicated When the

etiology is sympathetic hyperactivity, treatment with a

benzodiazepine should be prioritized Further treatment with a

combined alpha and beta blocker (labetalol), a calcium channelblocker (verapamil or diltiazem), or a combination of a beta blockerand a vasodilator (esmolol and nitroprusside) may be considered forcases refractory to high doses of benzodiazepines only when

adequate sedation has been achieved but cardiac conduction orblood pressure abnormalities persist Treatment with an α-

adrenergic antagonist (phentolamine) alone may sometimes beappropriate If the cause is anticholinergic poisoning, physostigminealone can be effective Supraventricular tachycardia without

hypertension is generally secondary to vasodilation or hypovolemiaand responds to fluid administration

For ventricular tachyarrhythmias due to tricyclic antidepressantsand other membrane-active agents (Table 459-1), sodium

bicarbonate is indicated, whereas class IA, IC, and III antiarrhythmicagents are contraindicated because of similar electrophysiologic

effects Although lidocaine and phenytoin are historically safe forventricular tachyarrhythmias of any etiology, sodium bicarbonateshould be considered first for any ventricular arrhythmia suspected

to have a toxicologic etiology Intravenous lipid emulsion therapyhas shown benefit for treatment of arrhythmias and hemodynamicinstability from various membrane-active agents Beta blockers can

be hazardous if the arrhythmia is due to sympathetic hyperactivity.Magnesium sulfate and overdrive pacing (by isoproterenol or a

pacemaker) may be useful in patients with torsades des pointes andprolonged QT intervals Magnesium and anti-digoxin antibodiesshould be considered in patients with severe cardiac glycoside

poisoning Invasive (esophageal or intracardiac) ECG recordingmay be necessary to determine the origin (ventricular or

supraventricular) of wide-complex tachycardias ( Chap 246 ) If thepatient is hemodynamically stable, however, it is reasonable to

simply observe the patient rather than to administer another

potentially proarrhythmic agent Arrhythmias may be resistant todrug therapy until underlying acid-base, electrolyte, oxygenation,and temperature derangements are corrected

Central Nervous System Therapies Neuromuscular hyperactivityand seizures can lead to hyperthermia, lactic acidosis, and

rhabdomyolysis and should be treated aggressively Seizures

caused by excessive stimulation of catecholamine receptors

(sympathomimetic or hallucinogen poisoning and drug withdrawal)

or decreased activity of GABA (isoniazid poisoning) or glycine

(strychnine poisoning) receptors are best treated with agents thatenhance GABA activity, such as benzodiazepine or barbiturates.Since benzodiazepines and barbiturates act by slightly differentmechanisms (the former increases the frequency via allosteric

modulation at the receptor and the latter directly increases the

duration of chloride channel opening in response to GABA), therapywith both may be effective when neither is effective alone Seizurescaused by isoniazid, which inhibits the synthesis of GABA at severalsteps by interfering with the cofactor pyridoxine (vitamin B6), mayrequire high doses of supplemental pyridoxine Seizures resultingfrom membrane destabilization (beta blocker or cyclic

antidepressant poisoning) require GABA enhancers

(benzodiazepines first, barbiturates second) Phenytoin is

contraindicated in toxicologic seizures: Animal and human datademonstrate worse outcomes after phenytoin loading, especially intheophylline overdose For poisons with central dopaminergic

effects (methamphetamine, phencyclidine) manifested by psychoticbehavior, a dopamine receptor antagonist, such as haloperidol orziprasidone, may be useful In anticholinergic and cyanide

poisoning, specific antidotal therapy may be necessary The

treatment of seizures secondary to cerebral ischemia or edema or

to metabolic abnormalities should include correction of the

underlying cause Neuromuscular paralysis is indicated in refractorycases Electroencephalographic monitoring and continuing

treatment of seizures are necessary to prevent permanent

neurologic damage Serotonergic receptor overstimulation in

serotonin syndrome may be treated with cyproheptadine

Other Measures Temperature extremes, metabolic abnormalities,hepatic and renal dysfunction, and secondary complications should

be treated by standard therapies

PREVENTION OF POISON ABSORPTION

Gastrointestinal Decontamination Whether or not to performgastrointestinal decontamination and which procedure to use

depends on the time since ingestion; the existing and predictedtoxicity of the ingestant; the availability, efficacy, and

contraindications of the procedure; and the nature, severity, and risk

of complications The efficacy of all decontamination proceduresdecreases with time, and data are insufficient to support or exclude

a beneficial effect when they are used >1 h after ingestion Theaverage time from ingestion to presentation for treatment is >1 h forchildren and >3 h for adults Most patients will recover from

poisoning uneventfully with good supportive care alone, but

complications of gastrointestinal decontamination, particularly

aspiration, can prolong this process Hence, gastrointestinal

decontamination should be performed selectively, not routinely, inthe management of overdose patients It is clearly unnecessarywhen predicted toxicity is minimal or the time of expected maximaltoxicity has passed without significant effect

Activated charcoal has comparable or greater efficacy; has

fewer contraindications and complications; and is less aversive andinvasive than ipecac or gastric lavage Thus, it is the preferred

method of gastrointestinal decontamination in most situations

Activated charcoal suspension (in water) is given orally via a cup,straw, or small-bore nasogastric tube The generally recommendeddose is 1 g/kg body weight because of its dosing convenience,

although in vitro and in vivo studies have demonstrated that

charcoal adsorbs ≥90% of most substances when given in an

amount equal to 10 times the weight of the substance Palatabilitymay be increased by adding a sweetener (sorbitol) or a flavoringagent (cherry, chocolate, or cola syrup) to the suspension Charcoaladsorbs ingested poisons within the gut lumen, allowing the

charcoal-toxin complex to be evacuated with stool Charged

(ionized) chemicals such as mineral acids, alkalis, and highly

dissociated salts of cyanide, fluoride, iron, lithium, and other

inorganic compounds are not well adsorbed by charcoal In studieswith animals and human volunteers, charcoal decreases the

absorption of ingestants by an average of 73% when given within 5min of ingestant administration, 51% when given at 30 min, and36% when given at 60 min For this reason, charcoal given beforehospital arrival by prehospital emergency medical services (EMS)increases the potential clinical benefit Side effects of charcoal

include nausea, vomiting, and diarrhea or constipation Charcoalmay also prevent the absorption of orally administered therapeuticagents, so the timing and the dose administered need to be

adjusted Complications include mechanical obstruction of the

airway, aspiration, vomiting, and bowel obstruction and infarctioncaused by inspissated charcoal Charcoal is not recommended forpatients who have ingested corrosives because it obscures

endoscopy

Gastric lavage should be considered for life-threatening poisons

that cannot be treated effectively with other decontamination,

elimination, or antidotal therapies (e.g., colchicine) Gastric lavage

is performed by sequentially administering and aspirating ∼5 mL offluid per kilogram of body weight through a no 40 French orogastrictube (no 28 French tube for children) Except in infants, for whom

normal saline is recommended, tap water is acceptable The patientshould be placed in Trendelenburg and left lateral decubitus

positions to prevent aspiration (even if an endotracheal tube is inplace) Lavage decreases ingestant absorption by an average of52% if performed within 5 min of ingestion administration, 26% ifperformed at 30 min, and 16% if performed at 60 min Significantamounts of ingested drug are recovered from <10% of patients.Aspiration is a common complication (occurring in up to 10% ofpatients), especially when lavage is performed improperly Seriouscomplications (esophageal and gastric perforation, tube

misplacement in the trachea) occur in ∼1% of patients For thisreason, the physician should personally insert the lavage tube andconfirm its placement, and the patient must be cooperative duringthe procedure Gastric lavage is contraindicated in corrosive orpetroleum distillate ingestions because of the respective risks ofgastroesophageal perforation and aspiration pneumonitis It is alsocontraindicated in patients with a compromised unprotected airwayand those at risk for hemorrhage or perforation due to esophageal

or gastric pathology or recent surgery Finally, gastric lavage is

absolutely contraindicated in combative patients or those who

refuse, as most published complications involve patient resistance

to the procedure

Syrup of ipecac, an emetogenic agent that was once the

substance most commonly used for decontamination, no longer has

a role in poisoning management Even the American Academy ofPediatrics—traditionally the strongest proponent of ipecac—issued

a policy statement in 2003 recommending that ipecac should nolonger be used in poisoning treatment Chronic ipecac use (by

patients with anorexia nervosa or bulimia) has been reported tocause electrolyte and fluid abnormalities, cardiac toxicity, and

myopathy

Whole-bowel irrigation is performed by administering a

bowel-cleansing solution containing electrolytes and polyethylene glycol(Golytely, Colyte) orally or by gastric tube at a rate of 2 L/h (0.5 L/h

in children) until rectal effluent is clear The patient must be in asitting position Although data are limited, whole-bowel irrigationappears to be as effective as other decontamination procedures in

volunteer studies It is most appropriate for those who have

ingested foreign bodies, packets of illicit drugs, and agents that arepoorly adsorbed by charcoal (e.g., heavy metals) This procedure iscontraindicated in patients with bowel obstruction, ileus,

hemodynamic instability, and compromised unprotected airways

Cathartics are salts (disodium phosphate, magnesium citrate

and sulfate, sodium sulfate) or saccharides (mannitol, sorbitol) thathistorically have been given with activated charcoal to promote therectal evacuation of gastrointestinal contents However, no animal,volunteer, or clinical data have ever demonstrated any

decontamination benefit from cathartics Abdominal cramps,

nausea, and occasional vomiting are side effects Complications ofrepeated dosing include severe electrolyte disturbances and

excessive diarrhea Cathartics are contraindicated in patients whohave ingested corrosives and in those with preexisting diarrhea.Magnesium-containing cathartics should not be used in patientswith renal failure

Dilution (i.e., drinking water, another clear liquid, or milk at a

volume of 5 mL/kg of body weight) is recommended only after theingestion of corrosives (acids, alkali) It may increase the dissolutionrate (and hence absorption) of capsules, tablets, and other solid

ingestants and should not be used in these circumstances.

Endoscopic or surgical removal of poisons may be useful in rare

situations, such as ingestion of a potentially toxic foreign body thatfails to transit the gastrointestinal tract, a potentially lethal amount of

a heavy metal (arsenic, iron, mercury, thallium), or agents that havecoalesced into gastric concretions or bezoars (heavy metals,

lithium, salicylates, sustained-release preparations) Patients whobecome toxic from cocaine due to its leakage from ingested drugpackets require immediate surgical intervention

Decontamination of Other Sites Immediate, copious flushingwith water, saline, or another available clear, drinkable liquid is theinitial treatment for topical exposures (exceptions include alkali

metals, calcium oxide, phosphorus) Saline is preferred for eye

irrigation A triple wash (water, soap, water) may be best for dermaldecontamination Inhalational exposures should be treated initiallywith fresh air or supplemental oxygen The removal of liquids from

body cavities such as the vagina or rectum is best accomplished byirrigation Solids (drug packets, pills) should be removed manually,preferably under direct visualization.

ENHANCEMENT OF POISON ELIMINATION

Although the elimination of most poisons can be accelerated bytherapeutic interventions, the pharmacokinetic efficacy (removal ofdrug at a rate greater than that accomplished by intrinsic

elimination) and clinical benefit (shortened duration of toxicity orimproved outcome) of such interventions are often more theoreticalthan proven Accordingly, the decision to use such measures should

be based on the actual or predicted toxicity and the potential

efficacy, cost, and risks of therapy

Multiple-Dose Activated Charcoal Repetitive oral dosing withcharcoal can enhance the elimination of previously absorbed

substances by binding them within the gut as they are excreted inthe bile, are secreted by gastrointestinal cells, or passively diffuse

into the gut lumen (reverse absorption or enterocapillary

exsorption) Doses of 0.5–1 g/kg of body weight every 2–4 h,

adjusted downward to avoid regurgitation in patients with decreasedgastrointestinal motility, are generally recommended

Pharmacokinetic efficacy approaches that of hemodialysis for someagents (e.g., phenobarbital, theophylline) Multiple-dose therapyshould be considered only for selected agents (theophylline,

phenobarbital, carbamazepine, dapsone, quinine) Complicationsinclude intestinal obstruction, pseudo-obstruction, and nonocclusiveintestinal infarction in patients with decreased gut motility Because

of electrolyte and fluid shifts, sorbitol and other cathartics are

absolutely contraindicated when multiple doses of activated

charcoal are administered

Urinary Alkalinization Ion trapping via alteration of urine pH mayprevent the renal reabsorption of poisons that undergo excretion byglomerular filtration and active tubular secretion Since membranesare more permeable to nonionized molecules than to their ionized

counterparts, acidic (low-pKa) poisons are ionized and trapped inalkaline urine, whereas basic ones become ionized and trapped in

acid urine Urinary alkalinization (producing a urine pH ≥7.5 and aurine output of 3–6 mL/kg of body weight per hour by the addition ofsodium bicarbonate to an IV solution) enhances the excretion ofchlorophenoxyacetic acid herbicides, chlorpropamide, diflunisal,fluoride, methotrexate, phenobarbital, sulfonamides, and salicylates.Contraindications include congestive heart failure, renal failure, andcerebral edema Acid-base, fluid, and electrolyte parameters should

be monitored carefully Although acid diuresis may make theoretical

sense for some overdoses (amphetamines), it is never indicated

and is potentially harmful

Extracorporeal Removal Hemodialysis, charcoal or resin

hemoperfusion, hemofiltration, plasmapheresis, and exchange

transfusion are capable of removing any toxin from the

bloodstream Agents most amenable to enhanced elimination bydialysis have low molecular mass (<500 Da), high water solubility,low protein binding, small volumes of distribution (<1 L/kg of bodyweight), prolonged elimination (long half-life), and high dialysis

clearance relative to total-body clearance Molecular weight, watersolubility, and protein binding do not limit the efficacy of the otherforms of extracorporeal removal

Dialysis should be considered in cases of severe poisoning due

to carbamazepine, ethylene glycol, isopropyl alcohol, lithium,

methanol, theophylline, salicylates, and valproate Although

hemoperfusion may be more effective in removing some of thesepoisons, it does not correct associated acid-base and electrolyteabnormalities, and most hospitals no longer have hemoperfusioncartridges readily available Fortunately, recent advances in

hemodialysis technology make it as effective as hemoperfusion forremoving poisons such as caffeine, carbamazepine, and

theophylline Both techniques require central venous access andsystemic anticoagulation and may result in transient hypotension.Hemoperfusion may also cause hemolysis, hypocalcemia, and

thrombocytopenia Peritoneal dialysis and exchange transfusion areless effective but may be used when other procedures are

unavailable, contraindicated, or technically difficult (e.g., in infants).Exchange transfusion may be indicated in the treatment of severearsine- or sodium chlorate–induced hemolysis,

methemoglobinemia, and sulfhemoglobinemia Although

hemofiltration can enhance elimination of aminoglycosides,

vancomycin, and metal-chelate complexes, the roles of

hemofiltration and plasmapheresis in the treatment of poisoning arenot yet defined

Candidates for extracorporeal removal therapies include patientswith severe toxicity whose condition deteriorates despite aggressivesupportive therapy; those with potentially prolonged, irreversible, orfatal toxicity; those with dangerous blood levels of toxins; those wholack the capacity for self-detoxification because of liver or renal

failure; and those with a serious underlying illness or complicationthat will adversely affect recovery

Other Techniques The elimination of heavy metals can be

enhanced by chelation, and the removal of carbon monoxide can beaccelerated by hyperbaric oxygenation

ADMINISTRATION OF ANTIDOTES

Antidotes counteract the effects of poisons by neutralizing them(e.g., antibody-antigen reactions, chelation, chemical binding) or byantagonizing their physiologic effects (e.g., activation of opposingnervous system activity, provision of a competitive metabolic or

receptor substrate) Poisons or conditions with specific antidotesinclude acetaminophen, anticholinergic agents, anticoagulants,

benzodiazepines, beta blockers, calcium channel blockers, carbonmonoxide, cardiac glycosides, cholinergic agents, cyanide, drug-induced dystonic reactions, ethylene glycol, fluoride, heavy metals,hypoglycemic agents, isoniazid, membrane-active agents,

methemoglobinemia, opioids, sympathomimetics, and a variety ofenvenomations Intravenous lipid emulsion has been shown to be asuccessful antidote for poisoning from various anesthetics and

membrane-active agents (e.g., cyclic antidepressants), but the

exact mechanism of benefit is still under investigation Antidotescan significantly reduce morbidity and mortality rates but are

potentially toxic if used for inappropriate reasons Since their safeuse requires correct identification of a specific poisoning or

syndrome, details of antidotal therapy are discussed with the

conditions for which they are indicated ( Table 459-4 )

TABLE 459-4 Pathophysiologic Features and Treatment of Specific Toxic Syndromes and Poisonings