⌘K
Volume 02

A study guide to toxicology.

For the resident who'd rather know the antidote before the page overhead. Toxidromes, overdoses, and the antidotes that reverse them, distilled. Last revised 2026.

11 topics

Toxicology

Toxidromes · Overdoses · Antidotes · Decontamination · Withdrawal

01

Initial Workup & Calculations

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Initial Workup & Calculations
Labs
Anion gap, osmolar gap, drug levels (paracetamol, salicylates, EtOH), βhCG
Anion gap
Na − Cl − HCO₃ · <12
Osmolar gap
Measured − calculated osmolality · <10
Calc. osm
2 × Na + Glucose + BUN

Consult poison control. Intentional OD › consult psychiatry.

02

TCA / Antihistamine Toxicity

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  • Features: blurry vision, mydriasis, flushed skin, hyperthermia, dry mouth, urinary retention, shaking, tachycardia, absent bowel sounds, hypotension, seizures, ↓LOC, agitation, psychosis, delirium, arrhythmia
  • ECG › wide QRS › VT/VF
  • ≤2h › activated charcoal 1 g/kg (max 50 g)
  • QRS >100 › NaHCO₃ 1–2 mEq/kg IV + infusion · pH 7.5–7.55 › IV MgSO₄ › lidocaine infusion
  • Refractory + unstable › lipid emulsion, VA ECMO
03

Salicylate Toxicity

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  • Features (1–2h): tinnitus, nausea, vomiting, hyperventilation, fever › coma, seizures, pulmonary edema, arrhythmia, thrombocytopenia, AKI
  • Toxic level >2.9–3.6 mmol/L · q2–4h
  • Respiratory alkalosis › HAGMA
  • ≤2h › activated charcoal 1 g/kg (max 50g)
  • NaHCO₃ infusion · pH 7.4–7.55, urine pH 7.5–8
  • HD indications: level >7.2 · hypoxemia · altered LOC · renal failure + level >6.5 · hemodynamic instability · persistent electrolyte/acid-base derangement (pH <7.2) · hepatic compromise + coagulopathy · volume overload preventing NaHCO₃ infusion
04

Paracetamol Toxicity

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  • Toxic: >250 mg/kg or >12 g in ≤12h · >350 mg/kg › severe liver toxicity
  • Stage I (30 min–24h): nausea, vomiting, diaphoresis, pallor, lethargy, malaise, asymptomatic
  • Stage II (24–72h): RUQ pain, jaundice, oliguria, ↑ AST/ALT
  • Stage III (72–96h): jaundice, hepatic encephalopathy, marked ↑ AST/ALT, coagulopathy, bili >68, hypoglycemia, lactic acidosis, hyperammonemia, bleeding, renal failure
  • Stage IV (96h–14d): recovery; hepatic necrosis may develop
  • Paracetamol level at 4h. ≤4h › activated charcoal 1 g/kg (max 50g)
  • NAC indications: level above treatment line on R-M nomogram · single ingestion >7.5 g (150 mg/kg) · unknown ingestion time + concentration >66 µmol/L · liver injury
  • NAC infusion reactions: mild flushing/urticaria › antihistamine or steroid; severe anaphylaxis/angioedema › stop infusion
  • DC NAC: INR <1.3 + ALT <100 + paracetamol level <132
05

Methemoglobinemia

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MetHb Levels & Features

MetHbFeatures
3–15%SpO₂ 90–95%, slate gray skin
15–20%Cyanosis, chocolate brown blood, SpO₂ 85%
20–50%Dizziness, syncope, fatigue, headache, weakness, dyspnea
>50%Coma, seizures, metabolic acidosis, arrhythmias, death
  • HbO₂ dissociation curve left-shifted · PaO₂ high, SpO₂ low (mismatch)
  • Causes: benzocaine, lidocaine, dapsone, nitrates, chloroquine, sulfonamides, hemolysis, Hb M, NADH MetHb reductase deficiency
  • Methylene blue 1–2 mg/kg CI G6PD, serotonin syndrome
06

Lithium Toxicity

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  • Features: N/V, diarrhea, dizziness, lethargy, slurred speech, ataxia, tremor, myoclonic jerks, hypernatremia
  • ECG › TW flattening · QT prolongation · bradycardia. WBC 15–20.
  • Whole bowel irrigation: SR formulation, symptomatic, unknown amount, >40 mg/kg, <6h, rising levels
  • HD indications: arrhythmias, seizures, severely abnormal mental status, level ≥5 mmol/L, level ≥4 mmol/L + Cr >176
  • IVF NS at 1.5× maintenance
07

Digoxin Toxicity

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  • Features: N/V, abdominal pain, delirium, fatigue, visual disturbances (blurred, halos), seizures, bradycardia, arrhythmias
  • ≤1h › activated charcoal
  • Digoxin-specific Fab (Digibind, Digifab) indications: dysrhythmias, hemodynamically unstable, K >5, severe GI symptoms, >10 mg, renal failure, altered LOC
08

Organophosphate Toxicity

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  • Decontamination · FiO₂ 100%
  • Muscarinic (DUMBELS): diaphoresis · diarrhea · urination · miosis · bronchospasm · bradycardia · bronchorrhea · emesis · lacrimation · salivation
  • Nicotinic (MATCH): muscle weakness/fasciculations · adrenergic stimulation (mydriasis) · tachycardia · CNS (lethargy, seizures, coma, resp depression) · HTN
  • Delayed neuropathy 1–3 weeks › painful stocking-and-glove paresthesia, symmetrical motor polyneuropathy
  • Atropine: 2 mg IV, double q3–5 min until pulmonary symptoms relieved + infusion
09

Opioid / Benzodiazepine / Sympathomimetic Toxicity

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  • Opioid OD: miosis, respiratory depression, lethargy, confusion, hypothermia, bradycardia, hypotension › naloxone, repeat PRN
  • Benzodiazepine OD: CNS depression › supportive care. Flumazenil › seizures.
  • Sympathomimetic (cocaine, amphetamines, MDMA): tachycardia, HTN, diaphoresis, agitation, seizures, mydriasis, hyperthermia › MI, rhabdomyolysis, renal failure, liver failure, CVA
    • Agitation / HTN › benzodiazepines
    • Cocaine + chest pain › ASA + nitroglycerin
    • MDMA/amphetamines › hyponatremia
10

Toxic Alcohols

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  • Alcohol poisoning: AKI, metabolic acidosis › NaHCO₃ infusion · pH 7.35
    • HD: end-organ dysfunction (seizures, coma, visual defects, renal failure), pH ≤7.15, persistent acidosis, high AG, very high parent alcohol level
  • Ethylene glycol: ↓LOC, frank hematuria, flank pain, oliguria, hypocalcemia, CN palsies, tetany, high AG and OG › fomepizole or ethanol + thiamine 100 mg IV + pyridoxine 50 mg IV
    • URM › calcium oxalate crystals
    • ECG › prolonged QTc (hypocalcemia)
  • Methanol: ↓LOC, blindness, afferent pupillary defect, mydriasis, retinal sheen, optic disc hyperemia, high AG and OG › fomepizole or ethanol + folic acid 50 mg IV QDS
  • Isopropyl alcohol / ethanol (raised OG, NAGMA) › supportive care
11

Carbon Monoxide & Cyanide Poisoning

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  • CO poisoning: HbO₂ curve left-shifted · SpO₂ overestimates 100% · HAGMA · lactic acidosis › remove source, ventilate, HFNC or MV FiO₂ 100%
    • Early (<4h): flu-like symptoms, frontal headache, lightheadedness, difficulty concentrating, nausea
    • End-organ hypoxia: arrhythmias, myocardial ischemia, CM, confusion, delirium, syncope, coma, dyspnea, pulmonary edema, cherry red skin, skin bullae, retinal hemorrhages
    • COHb >10% abnormal · CT/MRI › bilateral globus pallidus opacities
    • Hyperbaric O₂: within 6h exposure, COHb ≥25%, seizure/coma, syncope, persistent neuro deficits, pregnancy, cardiac ischemia
  • Cyanide: abrupt onset, bitter almonds smell, high VBG and ABG SaO₂, HAGMA, severe lactic acidosis › hydroxycobalamin 5 g IV over 15 min SE: anaphylactoid, HTN · acidosis › NaHCO₃