What is the appropriate management of atropine‑induced psychosis in a patient with organophosphate poisoning?

Management of Atropine-Induced Psychosis in OP Poisoning

For atropine-induced psychosis in organophosphate poisoning, administer physostigmine 1-4 mg by slow intravenous injection (0.5-1 mg in children), with benzodiazepines (diazepam or midazolam) as an alternative or adjunctive therapy for severe agitation and hallucinations. 1

Immediate Recognition and Differentiation

Atropine-induced psychosis manifests as restlessness, excitement, hallucinations, delirium, and potentially coma in severe cases 1. This can resemble an oneiroid syndrome and must be differentiated from the psychosis caused by the organophosphate itself, which presents with psychovegetative, psychovestibular, and hyperkinetic symptoms 2. The key distinction is that atropine toxicity occurs after therapeutic atropine administration and includes characteristic anticholinergic signs: dilated pupils, hot dry skin, thirst, difficulty swallowing, and absent bowel sounds 1.

Primary Antidote: Physostigmine

The FDA-approved antidote for atropine-induced delirium and coma is physostigmine, which rapidly abolishes these central nervous system effects 1. The dosing algorithm is:

• Adults: 1-4 mg by slow intravenous injection
• Pediatric patients: 0.5-1 mg by slow intravenous injection

Critical Caveats with Physostigmine

• Physostigmine is rapidly destroyed and patients may relapse into coma after 1-2 hours, requiring repeated doses 1
• Administer slowly to avoid cholinergic crisis
• Monitor closely for return of organophosphate toxicity symptoms, as physostigmine will worsen cholinergic crisis

Alternative Management: Benzodiazepines

For marked excitement and convulsions, short-acting barbiturates or diazepam may be used 1. This is particularly relevant given that:

• Benzodiazepines are already part of the organophosphate poisoning treatment protocol for seizure control 3, 4
• They provide sedation without the cholinergic effects of physostigmine
• Dosing: Diazepam 0.2 mg/kg or midazolam 0.1 mg/kg, repeated until symptoms resolve 3

Avoid large sedative doses, as central depressant action may coincide with the late depression occurring in atropine poisoning 1. Central stimulants are contraindicated 1.

The Atropinization Dilemma

This situation creates a clinical paradox: you need atropine to treat organophosphate poisoning, but excessive atropine causes psychosis. Do not stop atropine therapy prematurely just because of psychosis. Instead:

1. Titrate atropine to clinical endpoints: resolution of bronchorrhea, bronchospasm, and adequate oxygenation 3
2. In children, tachycardia is NOT a reason to stop atropine, as repeated boluses do not cause arrhythmias in pediatric patients (unlike adults) 3
3. Consider glycopyrrolate as an alternative anticholinergic that does not cross the blood-brain barrier, potentially avoiding CNS toxicity while controlling secretions 5

Supportive Measures

• Artificial respiration with oxygen may be necessary 1
• Fever management: ice bags and alcohol sponges, especially in children 1
• Continuous hemodynamic monitoring 3
• Note: Atropine is not removed by dialysis 1

Practical Algorithm

1. Recognize atropine toxicity: hot, dry, dilated pupils, delirium, hallucinations
2. Assess severity: mild agitation vs. severe delirium/coma
3. For severe delirium/coma: Physostigmine 1-4 mg IV slowly (adults) or 0.5-1 mg (children)
4. For agitation/convulsions: Diazepam or midazolam at standard doses
5. Monitor for relapse: Physostigmine effects wear off in 1-2 hours; repeat as needed
6. Continue organophosphate treatment: Don't stop atropine/oximes unless truly excessive
7. Consider glycopyrrolate for ongoing anticholinergic therapy without CNS effects

The fatal adult dose of atropine is unknown, but in children, 10 mg or less may be fatal 1, making careful dose monitoring essential in pediatric populations.