Emergency Medicine Hub / Toxicology & Environmental • 3 min read • 2 sections

Organophosphates, Carbamates & Nerve Agents

Comprehensive emergency evaluation and protocolized resuscitation of organophosphate insecticides, carbamates, and weaponized G- and V-series nerve agents (sarin, VX, tabun, novichoks): mechanism of acetylcholinesterase phosphorylation, the process of biochemical aging, muscarinic vs. nicotinic toxidrome distinction, massive atropinization protocols using pulmonary secretion drying endpoints, pralidoxime (2-PAM) dosing, and dual-agent autoinjectors (MARK I/CHEMPACK).

Resuscitation Quick Actions • First 2 Minutes

High-Acuity

Atropine Titration

Initial 2–5 mg IV push; DOUBLE the dose every 3–5 min (2 -> 4 -> 8 -> 16 -> 32 mg) until tracheobronchial secretions are bone dry

Atropinization Endpoints

Dry lung fields (clearing of rales/rhonchi), resolved bronchorrhea/wheeze, heart rate > 80 bpm, SBP > 90 mmHg (ignore mydriasis)

Pralidoxime (2-PAM)

1–2g IV in 100 mL NSS over 15–30 min, followed by continuous infusion at 500 mg/hr (pediatric 20–50 mg/kg then 10–20 mg/kg/hr)

Carbamate Distinction

Carbamates cause reversible carbamylation of AChE without aging; pralidoxime is generally unnecessary, but atropine is still mandatory

Seizure Control

Midazolam 10 mg IM/5–10 mg IV or Diazepam 10 mg IV stat; cholinergic seizures cause profound permanent excitotoxic brain injury

Decontamination First

Strip all clothing (removes 80–90% of dermal toxin), double-bag, and copiously irrigate skin with soap and warm water

Paraquat Toxicity

Bipyridyl herbicide causing lethal reactive oxygen species accumulation in pulmonary alveolar cells; leads to rapidly fatal progressive pulmonary fibrosis; DO NOT give supplemental O2 unless severely hypoxemic (oxygen accelerates paraquat-mediated lung injury!).

Bottom-Line Clinical Pearl

Organophosphates cause cholinergic crisis via irreversible covalent phosphorylation of acetylcholinesterase, producing deadly bronchorrhea and bronchospasm ('the killer Bs'). Primary cause of death is asphyxiation from drowning in secretions. Administer Atropine starting at 2–5 mg IV (pediatric 0.05 mg/kg), doubling the dose every 3–5 minutes until pulmonary endpoints are met: clear lung fields, dry bronchial secretions, and heart rate > 80 bpm (pupil size is NOT an endpoint!). Administer Pralidoxime (2-PAM) 1–2g IV over 30 min before 'aging' irreversibly bonds the enzyme.

1. Pathophysiology: Acetylcholinesterase Inhibition & Aging

Organophosphates (malathion, chlorpyrifos, parathion) and military chemical nerve agents (sarin [GB], soman [GD], tabun [GA], VX, and novichok agents) bind the active serine site of acetylcholinesterase (AChE), undergoing covalent phosphorylation. This arrests enzymatic breakdown of acetylcholine (ACh) at muscarinic, nicotinic, and central neural synapses, precipitating catastrophic cholinergic overstimulation.

Biochemical Aging: Over time, an alkyl group enzymatically dissociates from the phosphorylated AChE-organophosphate complex (a process termed aging). Once aging occurs, the bond becomes permanently irreversible; pralidoxime (2-PAM) can no longer reactivate the enzyme, leaving newly synthesized AChE (which takes weeks) as the only route to recovery. Aging times vary drastically: soman ages within 2 to 5 minutes (requiring immediate oxime administration), whereas sarin takes ~5 hours, and VX takes > 40 hours.

2. Clinical Presentation: DUMBELS & Nicotinic Features

Receptor Type & Location	Clinical Features & Toxidrome	Life-Threatening Emergency Hazards
Muscarinic (Parasympathetic Postganglionic)	DUMBELS: Defecation, Urination, Miosis, Bronchorrhea/Bronchospasm/Bradycardia ('Killer Bs'), Emesis, Lacrimation, Salivation	Asphyxiation from copious foaming pulmonary secretions and severe bronchospasm; profound bradycardia and AV nodal block.
Nicotinic (Sympathetic Ganglia & Neuromuscular Junction)	MTWTF: Mydriasis, Tachycardia, Weakness, Tremors, Fasciculations	Initial hypertension and tachycardia can mask muscarinic signs; progressive neuromuscular blockade leads to diaphragmatic and intercostal paralysis.
Central Nervous System (Central ACh Receptors)	Severe agitation, delirium, confusion, generalized seizures, central apnea, coma	Status epilepticus causes intense excitotoxic neuronal necrosis; seizures must be treated aggressively with high-dose benzodiazepines.

Critical Pitfall / Contraindication

SUCCINYLCHOLINE CONTRAINDICATION: Do NOT use succinylcholine for emergency intubation in organophosphate or nerve agent toxicity. Plasma pseudocholinesterase is completely inhibited; succinylcholine will produce prolonged neuromuscular paralysis lasting several hours to days. Use rocuronium (1.2–1.5 mg/kg IV) or sugammadex if rapid reversal is needed.

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