Oral Treatment of Propoxur Poisoning
Critical First Principle: Do NOT Use Pralidoxime
Pralidoxime (2-PAM) is contraindicated in carbamate poisoning, including propoxur, as it may increase toxicity. 1 The FDA drug label explicitly states that pralidoxime is not indicated for carbamate pesticide intoxication and may worsen carbaryl toxicity, a principle that extends to other carbamates like propoxur. 1
Immediate Management Algorithm
1. Decontamination (If Presenting Early)
- Remove all contaminated clothing immediately to prevent ongoing dermal absorption 2
- Do NOT induce vomiting with syrup of ipecac, as this can cause intractable emesis and delay definitive care 3
- Activated charcoal may be considered if the patient presents within 1 hour of ingestion with an intact or protected airway, though evidence for clinical benefit is limited 4
- Activated charcoal should NOT be given routinely, and is contraindicated without airway protection 4
2. Atropine: The Cornerstone of Treatment
Atropine is the primary antidote for propoxur poisoning and should be administered immediately for cholinergic symptoms. 2, 5
Dosing Protocol:
- Initial dose: 1-2 mg IV for adults (0.02-0.1 mg/kg for children) 2
- Double the dose every 5 minutes until bronchorrhea, bronchospasm, and bradycardia resolve 2
- Continue escalating doses until full atropinization is achieved (dry lungs, dry skin/mucous membranes, mydriasis) 2
- Maintain atropinization with continuous IV infusion after initial boluses 2
Critical Caveat:
- Atropine-induced tachycardia is NOT a contraindication to continued administration—the therapeutic endpoint is control of life-threatening muscarinic symptoms, not heart rate 2
- Tachycardia may actually result from nicotinic effects of the carbamate itself 2
3. Airway Management
- Early endotracheal intubation is recommended for life-threatening poisoning with respiratory distress or decreased consciousness 2, 6
- Avoid succinylcholine and mivacurium as neuromuscular blockers, since they are metabolized by cholinesterase 2
4. Benzodiazepines for Seizures and Agitation
- Administer benzodiazepines (diazepam or midazolam) for seizures, agitation, or to facilitate mechanical ventilation 2, 5
Key Distinction: Carbamates vs. Organophosphates
Propoxur is a carbamate that spontaneously dissociates from acetylcholinesterase, unlike organophosphates which cause permanent enzyme inactivation. 2 This fundamental difference explains why:
- Carbamate poisoning is generally shorter-acting and less severe than organophosphate poisoning 2
- Pralidoxime is not only unnecessary but potentially harmful in carbamate poisoning 1
- Supportive care with atropine alone is usually sufficient 2, 5
Alternative Agents for Atropine Allergy (Rare)
If a patient has documented severe allergic reaction to atropine (extremely rare):
- Glycopyrrolate (peripheral antimuscarinic) combined with benzodiazepines or scopolamine (for central effects) may be used 5
- This scenario is uncommon, as severe atropine allergy is rarely encountered despite extensive use 5
Monitoring and Supportive Care
- Continuous cardiac monitoring for dysrhythmias 2
- Serial respiratory assessments to monitor for bronchorrhea resolution 2
- Monitor cholinesterase activity, which will be inhibited but recovers spontaneously with carbamates 7
- Laboratory evaluation: Complete blood count, electrolytes, liver function tests, as propoxur can cause hepatotoxicity 8
- Observe for at least 48-72 hours for delayed complications 2
Common Pitfalls to Avoid
- Never administer pralidoxime for carbamate poisoning—this is the most critical error to avoid 1
- Do not stop atropine due to tachycardia—continue until muscarinic symptoms resolve 2
- Do not give activated charcoal without airway protection—aspiration risk is significant 4
- Do not delay atropine administration—immediate treatment is essential for severe cholinergic crisis 2