What is the immediate management of organophosphate poisoning?

Immediate Management of Organophosphate Poisoning

Administer atropine 1-2 mg IV immediately for adults (0.02 mg/kg for children, minimum 0.1 mg, maximum 0.5 mg per dose), doubling the dose every 5 minutes until full atropinization is achieved, while simultaneously giving pralidoxime 1-2 g IV over 15-30 minutes, securing the airway early, and performing thorough decontamination with appropriate personal protective equipment. 1, 2

Personal Protection and Decontamination (First Priority)

• Use full personal protective equipment before approaching the patient to prevent secondary contamination of healthcare workers—documented cases exist of providers requiring atropine, pralidoxime, and intubation after exposure to contaminated gastric contents or skin contact. 2
• Remove all contaminated clothing immediately and perform copious irrigation with soap and water (or sodium bicarbonate/alcohol) for any dermal exposure. 2, 3
• Never handle gastric contents, emesis, or perform gastric lavage without PPE—organophosphates in these materials have caused severe secondary poisoning requiring ICU admission. 2

Airway Management (Concurrent with Antidote Administration)

• Perform early endotracheal intubation for life-threatening poisoning, particularly when bronchorrhea, bronchospasm, or altered mental status threatens airway protection—observational data suggest better outcomes with early intubation. 1, 2
• Avoid succinylcholine and mivacurium as neuromuscular blockers because they are metabolized by cholinesterase and are contraindicated in organophosphate poisoning. 1, 2
• Provide supplemental oxygen and ventilatory support as needed, recognizing that respiratory failure is the primary cause of death. 2

Atropine Administration (Immediate Life-Saving Intervention)

Initial Dosing

• Give 1-2 mg IV bolus for adults immediately upon recognition of severe poisoning (bronchospasm, bronchorrhea, seizures, or significant bradycardia). 1, 2
• Give 0.02 mg/kg IV for children (minimum 0.1 mg, maximum single dose 0.5 mg per dose). 1, 2
• Do NOT give atropine in the presence of significant hypoxia due to risk of atropine-induced ventricular fibrillation—improve oxygenation first. 3

Dose Escalation Protocol

• Double the atropine dose every 5 minutes until full atropinization is achieved—this is NOT a fixed-dose schedule but an aggressive escalation protocol. 1, 2
• Therapeutic endpoints are: clear chest on auscultation (resolution of bronchorrhea), heart rate >80/min, systolic blood pressure >80 mmHg, dry skin and mucous membranes, and mydriasis. 1, 2
• Expect to use 10-20 mg in the first 2-3 hours for severe poisoning; some patients require up to 50 mg in the first 24 hours. 2

Maintenance Therapy

• Continue atropine as a continuous infusion at 10-20% of the total loading dose per hour (not exceeding 2 mg/hour in adults) once atropinization is achieved. 2
• Maintain some degree of atropinization for at least 48 hours until depressed blood cholinesterase activity is reversed. 3

Critical Management Principle for Tachycardia

• Atropine-induced tachycardia is an expected pharmacologic effect and is NOT a contraindication to continued administration—the therapeutic endpoint is control of life-threatening muscarinic symptoms, not heart rate normalization. 1, 2
• Tachycardia may originate from nicotinic receptor overstimulation by the organophosphate itself, not from atropine. 1
• The risk of undertreating organophosphate poisoning far exceeds the risk of atropine-induced tachycardia—inadequate atropinization leads to respiratory failure and death. 1

Pralidoxime (Oxime) Administration (Essential Concurrent Therapy)

Timing and Rationale

• Administer pralidoxime as soon as possible after atropine effects become apparent—ideally within minutes to hours before the organophosphate-acetylcholinesterase bond "ages" and becomes irreversible. 2, 3
• Pralidoxime reverses nicotinic effects (muscle weakness, fasciculations, respiratory muscle paralysis) that atropine cannot address. 1, 2
• The therapeutic window varies by agent: for nerve agents like soman, aging occurs within minutes; for agricultural organophosphates, a window of up to 24 hours exists, but efficacy drops by 50% after 6 hours. 2

Dosing Protocol

• Loading dose: 1-2 g IV for adults (25-50 mg/kg for children) administered slowly over 15-30 minutes, preferably by infusion. 1, 2, 3
• Maintenance infusion: 400-600 mg/hour for adults (10-20 mg/kg/hour for children) to maintain therapeutic plasma levels. 1, 2
• Do NOT withhold pralidoxime when the class of poison is unknown (organophosphate vs. carbamate)—organophosphate poisoning is clinically indistinguishable and requires early oxime therapy. 2

Evidence Level

• The American Heart Association gives pralidoxime a Class 2a recommendation with Level A evidence, meaning "it is reasonable to use" with high-quality evidence supporting efficacy. 2
• Treatment is most effective if initiated immediately—little is accomplished if pralidoxime is given more than 36 hours after exposure termination. 3

Seizure and Agitation Management

• Administer benzodiazepines for seizures and agitation: diazepam 0.2 mg/kg IV or midazolam 0.05-0.1 mg/kg IV in fractionated doses. 1, 2
• Benzodiazepines are first-line therapy for CNS manifestations and may facilitate mechanical ventilation. 2

Gastrointestinal Decontamination (When Ingestion Occurred)

• Perform gastric lavage with appropriate PPE if the patient presents within 1-2 hours of ingestion. 3
• Consider activated charcoal if the patient presents early and the airway is protected. 3
• Induce diarrhea to prevent continued absorption from the lower bowel—fatal relapses have been reported after initial improvement due to ongoing GI absorption. 3
• "Titrate" the patient with additional pralidoxime doses every 3-8 hours as long as signs of poisoning recur from continued GI absorption. 3

Monitoring and Supportive Care

• Continuous cardiac monitoring to detect dysrhythmias, not to limit atropine dosing. 1, 2
• Serial respiratory assessments every 5-10 minutes during the escalation phase to auscultate for bronchorrhea resolution. 1
• Monitor for at least 48-72 hours as delayed complications and relapses can occur, especially with ingested organophosphates. 1, 2, 3
• Establish IV access and administer fluids for volume resuscitation. 2
• Monitor creatine kinase and potassium levels for rhabdomyolysis detection—organophosphates can cause severe myonecrosis from calcium flux into skeletal muscle. 2

Complications to Anticipate

• Aspiration pneumonia from bronchorrhea—common and requires antibiotic coverage. 2
• Rhabdomyolysis with myoglobinuria causing renal damage—treat with adequate hydration, forced diuresis, and urine alkalinization when urine turns reddish (from myoglobin, not hemoglobin). 2
• Atropine-induced fever and hallucinations from high-dose therapy—expected adverse effects that do NOT indicate treatment failure and should NOT prompt discontinuation. 2
• Delayed muscle weakness (intermediate syndrome) can occur 4 days after acute exposure even as the initial cholinergic crisis resolves. 2

Drugs to Avoid

• Morphine, theophylline, aminophylline, reserpine, and phenothiazine-type tranquilizers should be avoided in organophosphate poisoning. 3
• Succinylcholine should be used with extreme caution if at all—prolonged paralysis has been reported when given with anticholinesterase activity. 3

Common Pitfalls to Avoid

• Never delay atropine administration—it is the immediate life-saving intervention with Class 1, Level A evidence. 2
• Never underdose atropine—organophosphate poisoning requires much higher doses than typical bradycardia treatment. 2
• Never stop atropine due to tachycardia—this is an expected effect and inadequate atropinization is lethal. 1
• Never withhold pralidoxime when the poison class is unknown—early oxime therapy is critical. 2
• Never allow healthcare workers to handle gastric contents without PPE—secondary poisoning is well-documented. 2

Contact Poison Control

• Call Poison Control (1-800-222-1222 in the US) for expert guidance on specific case management and antidote availability. 2