Why use it

Atropine is the PRIMARY life-saving antidote for cholinesterase inhibitor poisoning. Inadequate dosing leads to persistent respiratory secretions, bronchospasm, and respiratory failure — the primary cause of death. Overcalculated initial doses prevent treatment delays in severe cases. Note: Atropine does NOT reverse nicotinic effects (muscle weakness, paralysis) — pralidoxime (2-PAM) is required for this.

About

This calculator provides weight-based atropine dosing guidance for patients with cholinesterase inhibitor toxicity from organophosphate insecticides (e.g., malathion, parathion, chlorpyrifos), carbamate insecticides (e.g., carbaryl), or chemical warfare nerve agents (e.g., sarin, VX, novichok). Atropine is a competitive muscarinic antagonist that reverses the SLUDGE/DUMBELS syndrome (Salivation, Lacrimation, Urination, Defecation, GI distress, Emesis; Defecation, Urination, Miosis, Bradycardia, Emesis, Lacrimation, Salivation) caused by acetylcholine accumulation at muscarinic receptors. The clinical endpoint is DRYING OF SECRETIONS — NOT heart rate or pupil size. Large doses (far exceeding standard drug reference ranges) may be required in severe poisoning.

When to use

Suspected or confirmed organophosphate or carbamate insecticide poisoning with muscarinic symptoms
Chemical warfare nerve agent exposure (sarin, VX, novichok, tabun)
Excessive anticholinesterase drug toxicity (neostigmine, pyridostigmine overdose)
Any patient with SLUDGE or DUMBELS syndrome from a cholinergic toxidrome

Formula

Initial Atropine Dose: Adults (mild-moderate symptoms): 2–4 mg IV/IM, repeat every 5–10 minutes until secretions dry Adults (severe symptoms / respiratory compromise): Initial 4–8 mg IV; then 2–4 mg every 5–10 min until secretions dry Pediatric: 0.02–0.05 mg/kg IV/IM (minimum 0.1 mg, maximum 5 mg per dose) Repeat every 5–20 minutes until secretions dry Endpoint: DRY SECRETIONS + clear lung fields (not tachycardia) Pralidoxime (2-PAM) for organophosphates: Adults: 1–2 g IV over 15–30 min, then 200–500 mg/hr infusion Pediatric: 20–50 mg/kg IV over 15–30 min, then 10–20 mg/kg/hr

Pearls & pitfalls

CRITICAL: The endpoint of atropine therapy is DRYING OF SECRETIONS and clearing of bronchospasm — NOT tachycardia, not pupil dilation, not dry mouth.
In severe organophosphate poisoning, cumulative atropine doses of 20–100+ mg may be needed within the first hour — this is expected, not an overdose.
Pralidoxime (2-PAM) must be given EARLY (within hours) for organophosphate poisoning to reactivate acetylcholinesterase before irreversible "aging" occurs. It is NOT effective for carbamate poisoning.
Avoid succinylcholine for rapid sequence intubation — organophosphates inhibit pseudocholinesterase, causing prolonged paralysis. Use rocuronium instead.
Glycopyrrolate is NOT a substitute for atropine in this setting — it does not cross the blood-brain barrier and cannot reverse central nervous system cholinergic toxicity.
Benzodiazepines (diazepam, lorazepam) are essential for seizure management in organophosphate toxicity — do not delay.
Medical grade atropine auto-injectors (ATNAA) are used in military settings — 2 mg per injection, given sequentially.
Hyperglycemia commonly accompanies severe organophosphate poisoning due to catecholamine release and insulin suppression.
Intermediate syndrome (delayed onset 24–96h) can occur after organophosphate poisoning — manifests as proximal muscle weakness and respiratory compromise even after initial muscarinic syndrome resolves.

Next steps

CRITICAL ENDPOINT: Dry secretions (airway) — NOT heart rate, NOT pupil size. Repeat atropine every 5–10 minutes until secretions dry. Total doses in severe poisoning may exceed 100 mg. Give pralidoxime (2-PAM) simultaneously for organophosphate poisoning (not needed for carbamates). Secure airway early if secretions compromise breathing. Avoid succinylcholine for intubation (prolonged paralysis in organophosphate poisoning — use rocuronium). Decontaminate skin/eyes with copious water.

Evidence

Atropine as antidote for organophosphate poisoning established in 1950s military research. WHO Model List of Essential Medicines includes atropine as a core medicine. Multiple case series document requirement for very large doses (>50 mg) in severe poisoning. Roberts DM et al. (NEJM 2016) ATNAA trial; Eddleston M et al. extensive WHO-sponsored research on organophosphate poisoning in Asia.

References

Eddleston M et al. Evaluation of clinical signs to diagnose and grade the severity of acute organophosphorus insecticide poisoning. QJM. 2009;102(10):671-679. — link
Pawar KS et al. Continuous pralidoxime infusion versus repeated bolus injection to treat organophosphorus pesticide poisoning. Lancet. 2006;368(9553):2136-2141. — link
Worek F et al. Critical appraisal of 2-pyridinium aldoximes as antidotes for organophosphate poisoning. Arch Toxicol. 2004;78(1):7-15. — link

Atropine Dosing for Cholinesterase Inhibitor Toxicity

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