In which poisonings is atropine contraindicated?

Atropine Contraindications in Poisoning

Atropine has no absolute contraindications in organophosphate or nerve agent poisoning and should never be withheld in these life-threatening scenarios. 1 However, atropine is relatively contraindicated or requires extreme caution in certain specific poisoning contexts where its anticholinergic effects would worsen the underlying toxicity.

Poisonings Where Atropine Should Be Avoided

Anticholinergic Agent Poisoning

• Atropine is contraindicated in anticholinergic toxidromes (e.g., antihistamines, tricyclic antidepressants, scopolamine, jimsonweed) because it would exacerbate the existing anticholinergic syndrome—worsening hyperthermia, delirium, urinary retention, ileus, and potentially fatal cardiac arrhythmias. 2
• The treatment for anticholinergic poisoning is physostigmine (a cholinesterase inhibitor), which is the pharmacologic opposite of atropine. 2

Sympathomimetic Poisoning

• Atropine should be avoided in pure sympathomimetic toxicity (e.g., cocaine, amphetamines, ephedrine) where tachycardia and hypertension are already present, as atropine would further increase heart rate and potentially precipitate myocardial ischemia or arrhythmias.
• The tachycardia in sympathomimetic poisoning requires beta-blockade or benzodiazepines, not additional anticholinergic stimulation.

Thyrotoxicosis or Thyroid Storm

• Atropine is relatively contraindicated in thyrotoxic crisis because the existing hypermetabolic state with tachycardia, hyperthermia, and agitation would be dangerously worsened by atropine's anticholinergic effects.

Critical Context: When Atropine IS Indicated Despite Concerns

Organophosphate and Nerve Agent Poisoning

• Atropine is the gold standard, Class 1 Level A evidence treatment for organophosphate poisoning, with no absolute contraindications. 3, 1
• Even when tachycardia develops during treatment, atropine-induced tachycardia is NOT a contraindication to continued dosing—the therapeutic endpoint is control of bronchorrhea, bronchospasm, and adequate blood pressure, not heart rate normalization. 4
• Initial dosing: 1–2 mg IV for adults (0.02 mg/kg for children, minimum 0.1 mg, maximum 0.5 mg per dose), doubling every 5 minutes until full atropinization is achieved. 1, 5
• Cumulative doses may reach 10–20 mg in the first 2–3 hours, with some patients requiring up to 50 mg in 24 hours. 3, 5

Carbamate Poisoning

• Atropine is effective and recommended for carbamate poisoning (e.g., aldicarb, methomyl), providing protective ratios of 2–3 against lethality. 6
• The American Heart Association advises that oximes should not be withheld when the class of cholinesterase inhibitor is unknown (organophosphate vs. carbamate), though pralidoxime's benefit in pure carbamate poisoning is less clear. 1

Alternative Agents for Atropine Allergy

Rare Allergic Reactions

• Severe allergic reactions to atropine are extremely rare despite extensive use, with only scattered case reports in the literature documenting anaphylaxis. 7
• Most reactions are toxic (antimuscarinic) rather than allergic, related to interpersonal variation in sensitivity. 7

Recommended Alternatives

• For patients with proven atropine allergy, use glycopyrrolate (a peripheral antimuscarinic) combined with benzodiazepines or scopolamine (for central effects). 7
• Glycopyrrolate lacks central nervous system penetration, so concurrent benzodiazepines are essential to control central cholinergic toxicity and seizures. 7

Common Pitfalls to Avoid

• Never withhold atropine in organophosphate poisoning due to tachycardia—the risk of undertreating organophosphate poisoning (leading to respiratory failure and death) far exceeds the risk of atropine-induced tachycardia. 4
• Do not confuse anticholinergic poisoning with cholinergic poisoning—they require opposite treatments (physostigmine vs. atropine). 2
• Recognize that ophthalmic atropine can cause systemic anticholinergic toxicity through absorption, mimicking stroke or other neurologic emergencies. 2
• Always administer pralidoxime concurrently with atropine in organophosphate poisoning, as atropine reverses only muscarinic effects while pralidoxime addresses life-threatening nicotinic effects (muscle paralysis, respiratory failure). 3, 1