Organophosphate Poisoning - Drug Management

Mechanism of Toxicity

Organophosphates inhibit acetylcholinesterase (AChE) and pseudocholinesterase, causing accumulation of acetylcholine at:

Muscarinic receptors (parasympathetic postganglionic)
Nicotinic receptors (neuromuscular junction, autonomic ganglia)
CNS receptors (NMDA and cholinergic)

They are absorbed dermally, via ingestion, and by inhalation. A critical feature is aging - irreversible conformational binding of the organophosphate to AChE, after which oxime antidotes are no longer effective.

Clinical Toxidrome

SLUDGE / DUMBELS (Muscarinic effects):

SLUDGE	DUMBELS
Salivation	Diarrhea/Diaphoresis
Lacrimation	Urination
Urinary incontinence	Miosis
Defecation	Bradycardia/Bronchorrhea/Bronchospasm
GI cramps	Emesis
Emesis	Lacrimation
	Salivation

"Killer Bs" (most life-threatening muscarinic effects): Bradycardia, Bronchospasm, Bronchorrhea

Nicotinic effects: Tachycardia, tachydysrhythmias, muscle fasciculations, weakness, paralysis (including diaphragm - causes respiratory arrest)

CNS effects: Seizures, coma, agitation

4 Goals of Management

(Rosen's Emergency Medicine)

Decontamination
Supportive care (emphasis on respiratory stabilization)
Reversal of acetylcholine excess (Atropine)
Reversal of toxin binding at cholinesterase receptor sites (Pralidoxime/Oximes)

Step-by-Step Drug Management

1. DECONTAMINATION

Remove and destroy contaminated clothing
Thorough skin flushing with water (preferred)
Dry decontamination agents (flour, sand, bentonite) as alternatives
Gastric lavage and activated charcoal are NOT recommended - rapid absorption and GI symptoms negate benefit
Healthcare workers require level C PPE (full-face respirator, chemical-resistant suit, nitrile/butyl rubber gloves)

2. AIRWAY & SUPPORTIVE CARE

Suction secretions and vomitus
Supplemental oxygen; mechanical ventilation if needed
Intubation paralytic choice matters:
- Avoid succinylcholine if possible - metabolized by cholinesterases, may have prolonged effect (4-6 hours) in OP poisoning
- Prefer rocuronium 1 mg/kg (nondepolarizing, not metabolized by cholinesterases)
Do NOT treat tachycardia/tachydysrhythmias with beta-blockers - they resolve with treating cholinergic excess
Seizures/agitation/coma: Treat with benzodiazepines after airway is secured

3. ATROPINE - PRIMARY ANTIDOTE

Mechanism: Competitive antagonist at muscarinic receptors - blocks cholinergic overstimulation

Indication: Treats muscarinic signs (secretions, bronchospasm, bradycardia)

Parameter	Adult Dose	Pediatric Dose
Initial IV/IM	1-3 mg	0.05 mg/kg
Titration	Double dose every 5 minutes until effect	Same

Endpoint of atropinization (not pupil size):

Drying of secretions
Resolution of bronchospasm
HR > 80 bpm
NOT used to treat nicotinic effects (tachycardia, fasciculations)

Large doses may be needed in severe poisoning - doses of 10-20 mg or more over hours are not uncommon. Do NOT stop atropine prematurely.

4. PRALIDOXIME (2-PAM / Oxime) - CHOLINESTERASE REACTIVATOR

Mechanism: Cleaves the organophosphate-AChE bond, regenerating functional acetylcholinesterase - treats both muscarinic AND nicotinic effects

Critical caveat: Ineffective after aging has occurred (36-48 hours post-exposure in most OP insecticides; much faster with nerve agents like soman)

Parameter	Adult Dose	Pediatric Dose
IV intermittent	1-2 g over 30 min, repeat in 1-2 hr if weakness persists, then Q10-12 hr PRN	20-50 mg/kg (max 2000 mg), same interval
IV continuous	Loading 1-2 g, then infusion	Loading 20-50 mg/kg, then 10-20 mg/kg/hr (max 500 mg/hr)
IM (when IV unavailable)	600 mg Q15 min x3 (max 1800 mg)	<40 kg: 15 mg/kg Q15 min (max 45 mg/kg)

Combined auto-injector (Duodote/ATNNA): For patients >41 kg:

Mild symptoms: 1 prefilled syringe IM, wait 10-15 min
Severe symptoms: 3 prefilled syringes IM in rapid succession

Renal impairment: Reduce dose - 80-90% excreted unchanged in urine

Note: Pralidoxime is contraindicated in carbamate-only poisonings (generally), and is NOT effective for inorganic phosphates without anticholinesterase activity. Use only if severe carbamate poisoning or unable to differentiate from OP.

5. BENZODIAZEPINES (for seizures)

Diazepam or lorazepam IV are first-line for seizure control
Treat agitation and CNS effects alongside muscarinic reversal

6. GLYCOPYRROLATE (alternative to atropine)

A quaternary ammonium anticholinergic that does not cross the BBB
Can be used when atropine is unavailable; does not treat CNS effects
Dose titration to control secretions

A 2025 systematic review (PMID: 38797902) evaluated glycopyrrolate as an alternative to atropine in OP/carbamate poisoning - evidence supports its use but atropine remains standard of care.

Dosing Summary Table

Drug	Adult Dose	Pediatric Dose	Route	Notes
Atropine	1-3 mg initial; double Q5 min	0.05 mg/kg	IV/IM	Titrate to dry secretions
Pralidoxime	1-2 g bolus over 30 min	25-50 mg/kg	IV/IM	Give within 36-48 hr; repeat PRN
Rocuronium	1 mg/kg	1 mg/kg	IV	Preferred over succinylcholine for RSI
Benzodiazepine	Standard seizure dose	Standard	IV	For seizures, agitation, coma

Special Considerations

Issue	Management
Intermediate Syndrome (IMS)	Delayed muscle paralysis 24-96 hrs after cholinergic crisis resolves; watch respiratory muscles
Delayed peripheral neuropathy	7-21 days post-acute exposure; neurological follow-up
Rebound toxicity	May occur days later (lipid-stored OP release, e.g., fenthion); ICU admission
Succinylcholine avoidance	Prolonged paralysis (4-6 hr) due to reduced cholinesterase metabolism
Aging	Irreversible after 36-48 hr for most OP insecticides; nerve agents age within minutes

Disposition

Significant symptoms (seizures, respiratory compromise, depressed cholinesterase) → ICU admission
Asymptomatic/minimally symptomatic with near-normal cholinesterase → Observe 6 hours, discharge with close follow-up
Self-harm cases → Psychiatric consultation after medical stabilization

Sources:

Rosen's Emergency Medicine: Concepts and Clinical Practice, 9th ed., Ch. 152
The Harriet Lane Handbook, 23rd ed. (pralidoxime dosing)
Lippincott Illustrated Reviews: Pharmacology (mechanism and antidotes)
Rashid M et al. "Efficacy and Safety of Glycopyrrolate in the Management of Organophosphate and Carbamate Poisoning." Curr Rev Clin Exp Pharmacol 2025. [PMID: 38797902]

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