When to stop atropine in organophosphate (OP) poisoning?

When to Stop Atropine in Organophosphate Poisoning

Atropine should be continued until full atropinization is achieved and maintained for at least 48-72 hours, then gradually tapered based on resolution of muscarinic symptoms—never stop abruptly based on heart rate or fever alone. 1, 2

Specific Endpoints for Atropinization

Stop escalating atropine doses when ALL of the following clinical endpoints are achieved:

• Clear chest on auscultation (complete resolution of bronchorrhea) 2
• Heart rate >80 beats/min 2
• Systolic blood pressure >80 mm Hg 2
• Dry skin and mucous membranes 2
• Mydriasis (pupillary dilation) 2

Duration of Atropine Therapy

• Maintain atropinization for at least 48-72 hours after achieving full atropinization, as delayed complications and relapses can occur, especially with ingested organophosphates due to continued absorption from the GI tract 1, 2, 3
• The mean duration of atropine treatment in severe cases is approximately 9.6 days (range 1-24 days) 4
• Some degree of atropinization should be maintained until depressed blood cholinesterase activity is reversed 3

Maintenance Strategy After Initial Atropinization

• Switch to continuous atropine infusion after achieving initial bolus-dose atropinization to maintain therapeutic levels 1
• Titrate the patient with atropine as long as signs of poisoning recur—this is particularly critical with ingested organophosphates where fatal relapses have been reported after initial improvement 3
• Additional doses may be needed every 3-8 hours if symptoms recur 3

Critical Pitfalls: When NOT to Stop Atropine

Do Not Stop for Tachycardia

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

Do Not Stop for Fever

• Never withhold or prematurely discontinue atropine due to fever, as inadequate atropinization leads to respiratory failure and death 1
• Fever is an expected adverse effect with high-dose atropine therapy and does not indicate treatment failure 1
• Fever in organophosphate poisoning may have multiple etiologies beyond atropine, including nicotinic effects causing muscle fasciculations and aspiration pneumonia 1

Do Not Stop for High Cumulative Doses

• Atropine may reach cumulative doses of 50 mg in 24 hours before signs of full muscarinic antagonism appear in adults 5
• Cumulative doses of 10-20 mg in the first 2-3 hours are often necessary for adequate control 5
• Case reports document successful treatment with doses up to 11.6 grams over 12 days 6
• One case required almost 1000 mg total with full recovery 7

Gradual Tapering Protocol

• Once full atropinization is achieved and maintained for 48-72 hours, gradually reduce atropine doses rather than stopping abruptly 4
• Monitor closely during tapering for recurrence of muscarinic symptoms (bronchorrhea, bronchospasm, bradycardia) 2
• If symptoms recur during tapering, immediately escalate back to full atropinization 3

Essential Concurrent Monitoring

• Continuous cardiac monitoring to detect dysrhythmias, not to limit atropine dosing 2
• Serial respiratory assessments every 5-10 minutes during escalation phase 2
• Auscultate for bronchorrhea resolution as the primary respiratory endpoint 1
• Monitor for signs of atropine toxicity (delirium, hyperthermia, muscle twitching) which indicate adequate atropinization, not necessarily toxicity requiring cessation 3

Special Considerations for Ingested Organophosphates

• Prolonged treatment is required when organophosphates are ingested due to continued absorption from the lower bowel, which constitutes new exposure 3
• Fatal relapses have been reported after initial improvement in ingestion cases 3
• These patients require particularly vigilant monitoring and may need atropine for extended periods beyond the standard 48-72 hours 3, 7