Life-threatening toxicity from conium maculatum, or poison hemlock, is respiratory failure from nicotinic agonism.
What is Poison Hemlock?
Poison hemlock is found across the United States. It is a tall plant with a non-woody stem and clusters of small white flowers that coalesce into larger clusters. The stems are marked with red-purple macules which are often referred to as the “blood of Socrates,” an ancient Greek philosopher who is said to have died after being ordered to drink a concoction containing poison hemlock. In modern times, unsuspecting victims may consume poison hemlock after mistaking it for wild carrots, parsnips, sweet fennel, parsley, or the seeds of anise . Poison hemlock also has a similar appearance to cicutoxin-containing water hemlock, cicuta douglasii, whose primary toxicity results in seizures.
How would Poison Hemlock Poisoning present? [1-4]
Poison Hemlock contains coniine, -coniceine, and N-methyl-coniine which causes nicotine-receptor agonism.
The symptoms are due to initial excitation followed by depressed signaling in the central nervous system, the parasympathetic and sympathetic nervous systems, and motor pathways.
Patients may display a constellation of nausea, vomiting, respiratory secretion, urination, mydriasis, tachycardia or bradycardia, seizures, muscle fasciculations or tremor, weakness, and ataxia.
The greatest risk for morbidity and mortality results from weakness resulting in respiratory failure.
Rhabdomyolysis resulting in acute kidney injury has also been described.
A lethal dose may be 5-8 g of leaves .
How do you Treat Poison Hemlock Toxicity? [1-5]
Treatment of poison hemlock toxicity is largely supportive. Monitoring for respiratory failure is critical in case endotracheal intubation and mechanical ventilation are necessary due to respiratory muscle weakness. Gastrointestinal fluid losses resulting in dehydration and rhabdomyolysis should be treated with intravenous fluid administration. Treating muscarinic symptoms (bradycardia, bronchorrhea, or bronchospasm) with atropine can be considered, though high-level evidence for this treatment is lacking.
Bedside Pearls for Poison Hemlock Toxicity
Poison hemlock may be mistaken for edible species of plants or for water hemlock (also toxic).
Patients may present with both sympathetic and parasympathetic symptoms.
Gastrointestinal decontamination may be useful but close respiratory monitoring to prevent aspiration is required.
Expect dehydration from gastrointestinal fluid losses.
Atropine may be used to treat bronchorrhea, bradycardia, and bronchospasm.
Evaluate for rhabdomyolysis and acute kidney injury.
Close monitoring for respiratory failure or weakness that may require endotracheal intubation and mechanical ventilation is critical.
This post was peer reviewed on behalf of ACMT by Dr. Brent Furbee, Dr. Bryan Judge, and Dr. Louise Kao.
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Robert Goodnough, MD
Assistant Professor, Medical Toxicology
Department of Emergency Medicine, Baylor College of Medicine