17.1 Clinical Toxidromes & Initial Management of Acute Poisoning

Start with the patient, not the SDS

Handbook IV.10 and IV.11 sit in Domain IV (Applied Toxicology, 13% of the examination). Items here ask you to recognize a clinical toxidrome, to know what a laboratory gap is actually measuring, and to refuse the fantasy that a rodent LD50 or an occupational BEI tells the emergency physician when to intubate. Independent OpenExamPrep teaching in this section covers airway–breathing–circulation (ABCs), the coma cocktail and its traps, the cholinergic, anticholinergic, opioid, sympathomimetic, sedative-hypnotic, serotonin, and neuroleptic malignant clusters, anion and osmolar gaps, preclinical-to-clinical translation limits (IV.10 A), sources of reference values (IV.10 B), and a high-level therapeutic-dose versus overdose contrast for acetaminophen, digoxin, lithium, and theophylline (IV.8 A). This material is not an ABT, poison-center, or commercial-database product and does not claim official approval, review, or partnership with those bodies.

A formulation chemist carried out of a mixing room, a night-shift technician found in a locked restroom, and a foundry worker who drank washer fluid are the same examination skill: stabilize physiology, stop ongoing exposure, name the syndrome, then pick a mechanism-based antidote. Jumping to pralidoxime because the safety data sheet lists an organophosphate, while the patient is gurgling and blue, fails the first minute of care.

ABCs: the only sequence that is not optional

Airway. Listen for gurgling, stridor, and vomitus. If the patient cannot protect the airway, endotracheal intubation comes before charcoal, before a long toxidrome debate, and before most antidotes. Organophosphate bronchorrhea can fill the tube as fast as you place it; atropine that dries secretions is airway care, not a nicety.

Breathing. Count the respiratory rate and look at chest excursion. Opioid and sedative-hypnotic poisoning kill by hypoventilation and hypoxia. Bag-mask ventilation and oxygen do more in the first two minutes than any receptor antagonist. Pulse oximetry can look falsely reassuring in methemoglobinemia and is uninterpretable in the usual way in carbon monoxide exposure; a normal SpO2 does not prove adequate oxygen-carrying capacity.

Circulation. Pulse, blood pressure, and a 12-lead ECG belong in the primary survey. Wide QRS (tricyclic antidepressants, some sodium-channel blockers) changes the entire plan: sodium bicarbonate for the channel, not physostigmine. Hyperkalemia on the ECG in acute digoxin poisoning is a Fab clue, not a reason to push calcium the way you would in other hyperkalemia.

Disability and exposure. Fingerstick glucose, a temperature, pupils, skin moisture, muscle tone, and strip-and-irrigate if the chemical is still on the patient. The poisoned person is often still a source for staff. Remove clothing into sealed bags, wash skin with soap and water for most agents, and use copious water or saline for eyes. Do not "neutralize" an acid burn with a base on the skin.

The coma cocktail: what is still reasonable, and what is not

Older protocols bundled a coma cocktail for the unknown unresponsive adult: oxygen, dextrose, thiamine, and naloxone (sometimes remembered as DONT: dextrose, oxygen, naloxone, thiamine). The examination still tests the caveats, not nostalgia for a four-syringe ritual.

• Oxygen is almost always reasonable while you figure out the gas.
• Glucose. Hypoglycemia mimics every toxin. If you cannot get a rapid glucose, empiric dextrose is defensible. If you can measure, treat a low value rather than automatically pushing 50 mL of D50 in every coma.
• Thiamine. Give it to patients at risk of Wernicke encephalopathy (alcohol use disorder, malnutrition) when you give glucose. You are preventing an iatrogenic neurologic injury, not reversing a toxidrome.
• Naloxone. This is a competitive mu-opioid antagonist, not a general analeptic. Use it when the cluster is miosis plus hypoventilation. Start low in opioid-tolerant patients (precipitated withdrawal, vomiting, aspiration). It will not fix a benzodiazepine, a barbiturate, or a glycol ether.
• Do not add flumazenil to a shotgun cocktail. Flumazenil is a competitive antagonist at the benzodiazepine site on GABA-A. In a chronic benzodiazepine user, or in a mixed overdose that also contains a proconvulsant (tricyclic, cocaine, isoniazid), it can precipitate seizures that you then cannot easily stop with a benzodiazepine. Unknown coma is not a flumazenil indication.
• Do not add physostigmine as a diagnostic "wake-up." Physostigmine is a tertiary carbamate acetylcholinesterase inhibitor that crosses the blood–brain barrier. It has a narrow, later role in pure anticholinergic delirium with a narrow QRS. In tricyclic poisoning it has been associated with bradycardia, seizures, and asystole.

The modern translation: support the airway, measure glucose, give naloxone when the opioid toxidrome is present, give thiamine when the nutrition history demands it, and leave flumazenil and physostigmine off the unknown-coma tray.

Toxidromes: clusters, not single pathognomonic signs

A toxidrome is a reproducible constellation of vital signs, pupils, skin, secretions, bowel activity, and neuromuscular findings. One sign is never enough: miosis occurs in opioid, cholinergic, and some pontine injuries; mydriasis occurs in anticholinergic and sympathomimetic states. Read the cluster.

Cholinergic: DUMBBELS and SLUDGE. SLUDGE is salivation, lacrimation, urination, diarrhea, GI cramping, emesis. DUMBBELS is diarrhea, urination, miosis, bradycardia, bronchorrhea/bronchospasm, emesis, lacrimation, salivation/sweating. Those are muscarinic. Nicotinic features — fasciculations, weakness, then paralysis, and sometimes hypertension or tachycardia — explain why atropine alone does not restore the diaphragm. Organophosphates phosphorylate acetylcholinesterase and then age (lose an alkyl group), after which pralidoxime cannot regenerate the enzyme. Carbamates carbamylate the enzyme and generally do not age the same way; oxime is not the usual carbamate drug of first intent, but you still atropinize to dry the lungs. Do not wait for a red-blood-cell cholinesterase result to treat a crashing cholinergic patient.

Anticholinergic. The teaching rhyme is hot, dry, red, mad, blind, and full (urinary retention). The discriminator versus sympathomimetic is dry skin and quiet bowels versus sweat and active bowels. Both can be febrile, tachycardic, and mydriatic. That discriminator decides whether you even consider physostigmine later — and only after the ECG is not a sodium-channel story.

Opioid. The lethal cluster is miosis, bradycardia, hypothermia, and respiratory depression. Bowel sounds are decreased. There is no secretory storm. A pharmacy technician with a respiratory rate of 5, pulse 46, temperature 35.1 °C, and 1 mm pupils is an opioid problem until ventilation and naloxone say otherwise, even if someone mentions that pesticides also constrict pupils.

Sympathomimetic. Think wet, wild, and hot: diaphoresis, agitation, mydriasis, tachycardia, hypertension, hyperthermia. Cocaine adds sodium-channel and vasoconstrictive complications (wide QRS, ischemia). Amphetamines are more purely catecholaminergic. Cooling and benzodiazepines are the physiologic therapy; a beta blocker alone for cocaine chest pain is the classic wrong move because of unopposed alpha constriction.

Sedative-hypnotic. The patient is down, with relatively unimpressive pupils and skin. Respiratory depression still kills. This is where people reach for flumazenil; the examination wants you to ventilate and to remember the seizure risk of reversing a chronic benzodiazepine or a mixed overdose.

Serotonin syndrome versus NMS. Hunter decision rules hinge on clonus (inducible, spontaneous, or ocular) in the presence of a serotonergic agent, plus agitation, diaphoresis, hyperreflexia, and hypertonia that is often lower-limb predominant. Onset is usually hours. NMS is a hypodopaminergic rigidity syndrome: lead-pipe tone, reduced reflexes, slower evolution over days, often after a new antipsychotic or a dose increase, or after stopping a dopaminergic drug in Parkinson disease. Both can be hyperthermic. The treatment implications differ (cyproheptadine and sedation/cooling versus bromocriptine/dantrolene discussions and stopping the antipsychotic), but the DABT discriminator is the neuromuscular exam and the time course, not a single creatine kinase value.

Anion gap and osmolar gap

Two calculated gaps convert a metabolic panel into a toxic-alcohol hypothesis.

Anion gap ≈ Na⁺ − (Cl⁻ + HCO₃⁻). Many laboratories' normal mean sits near 8–12 mEq/L; use the laboratory's reference and albumin (hypoalbuminemia lowers the observed gap). A high anion-gap metabolic acidosis in poisoning classically includes methanol (formate), ethylene glycol (glycolate, oxalate), salicylate, lactic acid (seizure, shock, cyanide, metformin, carbon monoxide), and others remembered with teaching mnemonics. The mnemonic is a memory aid; the physiology is unmeasured anions.

Calculated osmolarity (conventional US units) ≈ 2×Na + glucose/18 + BUN/2.8 + ethanol/4.6 (some use ethanol/4.6 mg/dL per mOsm; confirm the factor the laboratory uses). Osmolar gap ≈ measured osmolality − calculated osmolarity. A gap of about 10–15 mOsm/kg can be "normal" depending on the formula; a gap of 20–25 or more with a compatible history is a parent low-molecular-weight alcohol signal (methanol, ethylene glycol, isopropanol, propylene glycol, ethanol if you forgot to include it).

Worked example. Na 140 mEq/L, glucose 90 mg/dL, BUN 14 mg/dL, ethanol 0. Calculated osmolarity = 280 + 5 + 5 = 290 mOsm/L. Measured osmolality 340 mOsm/kg. Gap 50. Early after methanol or ethylene glycol, the gap is the parent alcohol; as alcohol dehydrogenase generates acids, the anion gap rises and the osmolar gap falls. Isopropanol is metabolized to acetone, which is osmotically active but not an acid: high osmolar gap, ketosis, little anion-gap acidosis. That pattern is why "any osmolar gap means give fomepizole and call dialysis for ethylene glycol" is too crude — you still treat a sick methanol/EG picture empirically, but you interpret acetone-without-acidosis as isopropanol until proven otherwise.

Salicylate is a high-anion-gap, often mixed respiratory alkalosis plus metabolic acidosis story, not primarily an osmolar-gap alcohol. Do not force every acidosis into a toxic-alcohol box.

Preclinical-to-clinical translation limits (IV.10 A)

Applied toxicology still starts in animals and in vitro, but IV.10 A is the warning label on that pipeline.

LD50 is not a toxidrome. A rat oral LD50 tells you relative potency in that protocol. It does not tell you whether the human dies of bronchorrhea, torsades, hepatic necrosis, or cerebral edema. Species differences in carboxylesterases, plasma butyrylcholinesterase, CYP2E1, and alcohol dehydrogenase isoforms change both the metabolite and the time course. An oxime that regenerates rodent acetylcholinesterase in a bench assay may be too late for a rapidly aging nerve agent in a human.

In vitro IC50 is not a dose. Naloxone's receptor Ki does not set the milligram titration in a fentanyl analog overdose. Methylene blue's catalysis of NADPH methemoglobin reductase does not work if the patient has G6PD deficiency and cannot make NADPH. Fomepizole's Ki for ADH does not clear already-formed formate; that is why hemodialysis still has a role.

Volunteer studies use subtoxic doses. Pharmacokinetics of oral N-acetylcysteine in healthy adults are not the same as IV NAC in late-presenting acute liver failure with vomiting, third-spacing, and impaired glutathione synthesis. Therapeutic-index numbers from repeat-dose GLP studies do not predict idiosyncratic human syndromes such as NMS and serotonin syndrome, which are poorly reproduced in standard rodent batteries.

Occupational and emergency air numbers are not serum treatment thresholds. An AEGL and a BEI can be scientifically excellent and still be the wrong instrument at the bedside (next subsection). Translation failure on the exam looks like: "the 4-hour rat LC50 was 200 ppm, therefore start hemodialysis."

Sources of reference values (IV.10 B)

You will be asked where a number came from and what question it answers. Handbook IV.10 B expects you to know the families, not to memorize a vendor price list.

Poison-information systems. Certified poison centers and medical toxicologists use computerized monographs that compile dose, kinetics, clinical features, and antidotes (Poisindex-type files historically distributed inside larger clinical knowledge bases such as Micromedex). Treat those names as examples of a class: structured, frequently updated clinical toxicology references used to support case management. They are not a product OpenExamPrep or ABT requires you to purchase, and citing a brand is not a substitute for knowing the physiology. Primary literature, national poison-data systems, and bedside toxicology texts occupy the same conceptual shelf: clinical reference, not an OSHA PEL.

AEGLs (Acute Exposure Guideline Levels). These are community airborne values for rare accidental releases, at AEGL-1/2/3 and durations from 10 minutes to 8 hours, including susceptible people. They help decide evacuation or shelter. They are not a serum concentration at which you give an antidote and not an 8-hour worker PEL.

Occupational BEIs (Biological Exposure Indices). ACGIH BEIs are guidance values for determinants in blood, urine, or exhaled air, typically in healthy workers with inhalation at the TLV, collected at a specified time (end of shift, end of week). A BEI exceedance is a hygiene and route-of-entry problem. It is not, by itself, an emergency-department treatment trigger and not a legal OSHA PEL.

Therapeutic ranges (TDM). These are clinical laboratory intervals associated with usual efficacy and rising adverse-effect risk: for example, many laboratories still quote lithium near 0.6–1.2 mEq/L for maintenance, digoxin often <1.0 ng/mL in contemporary heart-failure practice (older texts used a higher ceiling near 2 ng/mL), theophylline historically 10–20 µg/mL. They are not bright lines of safety: a "therapeutic" acetaminophen concentration 4 hours after a massive ingestion can still sit above the Rumack–Matthew treatment line, and a "therapeutic" lithium level does not forbid neurotoxicity in the elderly or in dehydration. The acetaminophen nomogram is a timed, single-acute-ingestion tool, not a chronic-supratherapeutic tool.

Common therapeutics: side effect versus overdose (IV.8 A, high level)

Acetaminophen. At labeled doses, most adults tolerate up to 4 g/day; nausea can occur without liver failure. Overdose (often ≥7.5–10 g acutely in an adult, less in high-risk patients) overwhelms glucuronidation/sulfation, shunts to CYP2E1, and produces NAPQI. When glutathione is depleted, NAPQI binds hepatocellular proteins → centrilobular necrosis. Chronic heavy ethanol use induces CYP2E1 and can deplete GSH, so injury at near-therapeutic doses is a recognized pattern. Antidote logic is in 17.2: N-acetylcysteine as a GSH precursor.

Digoxin. Therapeutic nuisance effects include mild nausea and vague visual complaints. Overdose of this Na⁺/K⁺-ATPase inhibitor produces hyperkalemia (acute), bradyarrhythmias, ventricular ectopy, bidirectional ventricular tachycardia, and gastrointestinal and visual toxicity. Chronic toxicity may present with a less dramatic potassium. Digoxin-specific Fab binds free drug; total digoxin assays after Fab are misleadingly high.

Lithium. A fine tremor and polyuria can appear inside the TDM window (nephrogenic diabetes insipidus physiology). Overdose — especially chronic toxicity in a volume-depleted patient — adds coarse tremor, clonus, seizures, altered mentation, and risk of permanent cerebellar injury. Lithium is a small cation: charcoal does not bind it. Hemodialysis is the enhanced-elimination tool when levels and neurologic severity demand it.

Theophylline. Narrow therapeutic index: insomnia, tremor, and nausea appear as concentrations climb through the historic 10–20 µg/mL window. Overdose adds seizures, hypokalemia, hyperglycemia, and tachyarrhythmias (adenosine antagonism plus catecholamine release). Multi-dose charcoal and hemodialysis appear in 17.2 because the mechanism is systemic adenosine/PDE effects, not a receptor you reverse with a single Fab-like molecule.

Integrated bedside vignette

A 28-year-old research associate is found next to a spilled vial and an unlabeled squeeze bottle. RR 28 then 8, HR 40, wet lungs, pinpoint pupils, fasciculations, and diarrhea. A coworker insists "it must be fentanyl; give naloxone and go home." Another coworker waves an SDS for a carbamate. You open the airway, suction bronchorrhea, atropinize to dry secretions, and only then sort opioid versus cholinergic. Naloxone that does not restore ventilation, plus secretions and fasciculations, is cholinergic, not opioid. If the agent is an organophosphate, pralidoxime is added because nicotinic neuromuscular failure is an aged-or-aging enzyme problem, not a mu-receptor problem. Glucose was already checked. Flumazenil was never on the table. That sequence — ABC, toxidrome, then mechanism — is the IV.10/11 skill.

Exam traps

• Treating miosis as pathognomonic for one class.
• Adding flumazenil or physostigmine to an unknown coma.
• Using a BEI or AEGL as a serum treatment threshold.
• Calling every osmolar gap ethylene glycol when acetone without acidosis is isopropanol.
• Equating a rodent LD50 with a human antidote dose.
• Calling a therapeutic lithium or theophylline level proof that the patient is not poisoned.

Key takeaways

• ABCs and stopping exposure precede antidotes; the coma cocktail is not flumazenil or physostigmine.
• Toxidromes are clusters: DUMBBELS/SLUDGE versus dry anticholinergic versus opioid hypoventilation versus clonus versus lead-pipe NMS.
• Follow the anion and osmolar gaps through toxic-alcohol metabolism.
• Preclinical and occupational numbers do not automatically become bedside cutoffs.
• Poison-information files, AEGLs, BEIs, and TDM ranges answer different questions.