Organophosphate Poisoning — Atropine and Pralidoxime

Key Points

• Treat the clinical cholinergic toxidrome immediately; do not wait for cholinesterase assay results.
• Bronchorrhea and bronchospasm are the most important atropine targets, not pupil size.
• Atropine doses often need rapid escalation and may be much larger than routine bradycardia dosing.
• Pralidoxime is most useful when given early in meaningful organophosphate poisoning and does not replace atropine.
• Protect staff from secondary contamination and remove contaminated clothing before routine handling when feasible.
• Use benzodiazepines for seizures; airway and ventilatory support remain essential.
• Avoid assuming clinical improvement is permanent because intermediate neuromuscular weakness can emerge later.
• Succinylcholine paralysis may be prolonged; choose neuromuscular blockade thoughtfully during intubation.

Algorithm

1. Protect rescuers and remove the patient from the exposure source.
2. Perform airway, breathing, and circulation assessment while beginning skin and clothing decontamination when needed.
3. Recognize the combination of bronchorrhea, bronchospasm, miosis, bradycardia, gastrointestinal hyperactivity, fasciculations, or weakness.
4. Give IV atropine and rapidly escalate doses until pulmonary secretions and bronchospasm improve.
5. Give pralidoxime early for clinically important organophosphate poisoning and continue according to toxicology protocol.
6. Treat seizures with benzodiazepines and provide ventilatory support when respiratory effort is inadequate.
7. Transition to atropine infusion when repeated boluses are required and monitor for recurrent cholinergic findings.
8. Admit significant exposures and monitor for respiratory weakness, aspiration, dysrhythmia, and intermediate syndrome.

Clinical Synopsis & Reasoning

Organophosphates are found in agricultural insecticides and nerve agents. Acetylcholinesterase inhibition causes excess acetylcholine at muscarinic, nicotinic, and central nervous system synapses. Muscarinic findings include salivation, lacrimation, urination, diarrhea, vomiting, miosis, bradycardia, bronchospasm, and especially bronchorrhea. Nicotinic effects include fasciculations, weakness, paralysis, and sometimes tachycardia or hypertension. Central effects include agitation, confusion, seizure, and coma.

The immediate cause of death is usually respiratory failure from a combination of airway secretions, bronchoconstriction, central respiratory depression, and neuromuscular weakness. Diagnosis is clinical. Do not wait for cholinesterase levels before treating a compatible toxidrome. Clothing, skin, and vomitus can contaminate rescuers, so staff protection and decontamination are part of resuscitation. Remove contaminated clothing and irrigate exposed skin while protecting the airway and preventing secondary exposure.

Consider carbamate toxicity, nicotine, mushroom poisoning, clonidine, opioid poisoning, pontine injury, and other causes of miosis or secretions. Cholinesterase assays can support the diagnosis but may not be rapidly available and do not guide minute-to-minute atropine dosing. ECG, electrolytes, glucose, blood gas, chest imaging, and other testing are directed at respiratory failure, aspiration, dysrhythmia, and coexposures.

Treatment Strategy & Disposition

Atropine is the first-line antidote for life-threatening muscarinic effects. Give an initial IV dose appropriate to severity and rapidly double or escalate every few minutes until bronchorrhea and bronchospasm improve, oxygenation and ventilation are adequate, and hemodynamics are acceptable. The endpoint is drying of dangerous pulmonary secretions and improved respiratory physiology, not normalization of pupil size or heart rate. Very large cumulative doses may be required in severe pesticide or nerve-agent poisoning.

Pralidoxime reactivates acetylcholinesterase before the enzyme-organophosphate complex ages and is used early in clinically significant poisoning, particularly with weakness, fasciculations, respiratory compromise, or substantial exposure. A common adult approach is 1 to 2 g IV over 15 to 30 minutes followed by repeated dosing or continuous infusion according to toxicology guidance and local protocol. Benzodiazepines are used for seizures and severe agitation. Intubation may be required, and succinylcholine can have prolonged effects because cholinesterase activity is inhibited, so a nondepolarizing paralytic is often preferred.

After atropinization, recurrent secretions may require an atropine infusion titrated to respiratory findings. Admit symptomatic patients, and monitor for intermediate syndrome with delayed proximal and respiratory muscle weakness after initial cholinergic symptoms improve. Patients with deliberate ingestion require psychiatric assessment after medical stabilization. Occupational and household exposures require decontamination and prevention review.

Epidemiology / Risk Factors

• Agricultural workers, pesticide applicators, and people in regions with ready pesticide access are at increased exposure risk.
• Intentional self-poisoning with concentrated agricultural organophosphates can produce particularly severe and prolonged toxicity.
• Nerve agents are organophosphorus compounds that produce the same core cholinergic physiology but may require disaster and decontamination protocols.
• Dermal exposure can cause delayed onset because absorption continues through contaminated clothing or skin.
• Children may present after household pesticide exposure and can have prominent neurologic rather than classic secretory findings.

Investigations

Therapy Overview

Pharmacology

Prognosis / Complications

• Outcome depends on dose, route, delay to treatment, respiratory failure, aspiration, and availability of ventilatory support.
• Most survivors recover when atropine, oxime therapy, and respiratory support are provided promptly.
• Intermediate syndrome can cause delayed respiratory muscle weakness one to several days after acute symptoms improve.
• Some organophosphates are associated with delayed peripheral neuropathy weeks after exposure.
• Severe hypoxic injury or prolonged seizures worsen neurologic prognosis.

Patient Education / Counseling

• Explain that contaminated clothing should be handled carefully and washed or discarded according to public-health or hazardous-material guidance.
• Workers should review protective equipment, pesticide storage, labeling, and application practices before returning to exposure settings.
• Household pesticides should be kept in original containers and away from children and food products.
• Return precautions after discharge should include weakness, difficulty breathing, recurrent sweating or secretions, confusion, or new neurologic symptoms.
• Intentional exposure requires mental-health evaluation and safe storage planning before discharge.
• Patients with severe poisoning should receive follow-up for delayed weakness or neuropathic symptoms.

Notes

The practical bedside endpoint for atropine is respiratory. If the patient remains hypoxic with copious secretions, atropine is not adequate merely because the heart rate has risen or the pupils have changed.

Because compound potency, formulation, route, and aging kinetics differ, severe cases benefit from continuous toxicology consultation rather than rigid adherence to one total antidote dose.

References

1. American Heart Association 2025 Special Circumstances of Resuscitation — Link
2. CDC Chemical Emergencies Resources — Link