IDENTIFICATION
The correct identification of this plant is imperative. If the identity is uncertain, seek clarification from a reliable source such as a garden center or botanist. |
Different Conium species cause different toxic effects. Generalizations should never be made as to symptoms expected. “Hemlock” may refer to Conium maculatum or Cicuta spp.. Both are highly toxic but have very different effects.   |
COMMON NAME(S)
California fern | Carrot fern | Deadly hemlock | Giftkjets | Hemlock | Nebraska fern | Poison hemlock | Poison parsley | Skarntyde | Spotted hemlock | Winter fern | |
NB: The common names of Conium maculatum are also used to refer to other genera in the Umbelliferae family. Botanic identification is crucial. |
“Hemlock” most commonly refers to Conium maculatum (poison hemlock) but can refer to Cicuta spp. (water hemlock), which are related and significantly toxic, but contain different toxic components. Although many symptoms overlap, differentiation is important; in severe poisoning Conium maculatum causes respiratory paralysis, whereas Cicuta spp. plants result in profound seizures and potentially status epilepticus.   |
HABITAT
Conium maculatum is native to Europe and West Asia. It has been introduced to America, North Africa, Australia, and New Zealand. |
USES
Extracts of this species were used both as a sedative and an antispasmodic. However, because of the plants toxicity, it was discontinued by the early 20th century. |
This species has no known uses and is classified as a weed.
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INTERVENTION CRITERIA
Decontamination, if appropriate, and monitoring is recommended: - For all known or suspected ingestions of hemlock With environmental exposures involving dermal contact, management depends on clinical presentation. Refer all symptomatic cases to an appropriate health care facility. |
All patients require medical attention. |
If medical observation is required, the patient must be observed for 4 hours following exposure for onset or worsening of symptoms. |
If the patient is asymptomatic at the end of the observation period, and if they have been appropriately decontaminated and any investigations have been completed, they may be: Discharged into the care of a reliable observer, or Referred for psychological assessment if the overdose or exposure was with intent to self-harm |
A mousy odor is associated with Conium maculatum; this odor on the breath or in the urine can be used as a diagnostic clue. However, absence of this odor does not rule out exposure. |
Coniine (or other plant alkaloids) blood levels are not readily available, nor necessary for clinical management.
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Admission to an intensive care facility is required for those suffering significant signs of toxicity including: CNS depression Convulsions Respiratory depression Hypotension Bradycardia |
TREATMENT
TREATMENT SUMMARY
Administration of activated charcoal may be considered within one hour of ingestion; however, benefit is unproven, and risks of seizure, vomiting, and aspiration potentially out-weigh gain.  There are no specific antidotes and no methods for enhancing elimination can be recommended. Supportive care is the mainstay of management with primary emphasis on cardiovascular and respiratory support. In severe cases, particular care should be given to airways management and respiratory support is vital in obtaining a positive outcome, as death is usually due to respiratory paralysis. Routine supportive care should be used for the treatment of other effects. Nausea and vomiting may persist requiring symptomatic care with IV rehydration or antiemetic drugs, appropriate fluid and electrolyte balance must be maintained. Hypotension usually responds to intravenous fluids, sympathomimetics may be needed. Rarely cardiac dysrhythmias occur and should be managed using standard electrical and/or pharmacological methods. Extreme agitation or seizures can be a complicating feature and should be treated with a benzodiazepine. Atropine may be used to control manifestations from parasympathetic stimulation, such as diarrhea, urination, bronchospasm, emesis, lacrimation, and sweating. Monitor for rhabdomyolysis and acute renal failure. |
EMERGENCY STABILIZATION
Ensure Adequate Cardiopulmonary Function |
Ensure the airway is protected if compromised (intubation may be necessary). |
Immediately establish secure intravenous access. |
Administer a benzodiazepine as first-line treatment to patients with seizure activity.  Blood glucose concentration should be promptly determined. If the result indicates hypoglycemia, or is unobtainable, supplemental dextrose should be administered IV. |
Heart rate Respiratory rate Seizure activity
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DECONTAMINATION
Single Dose Activated Charcoal |
Decontamination with activated charcoal is recommended for recent ingestions of hemlock. However, as hemlock commonly produces vomiting, CNS or respiratory depression, the time frame for successful administration is limited and risks pulmonary aspiration. In symptomatic patients general supportive measures should take precedence over decontamination.  |
Administer activated charcoal up to 1 hour following a potentially toxic ingestion.  |
Single dose activated charcoal CHILD 1 to 2 g/kg orally ADULT 50 to 100 g orally |
Nasogastric Administration |
Nasogastric instillation of activated charcoal is not recommended unless the ingestion is potentially severely toxic and oral administration is not possible. Confirmation of accurate placement of the nasogastric tube after airway protection is secured must be ensured. |
If necessary, remove contaminated clothing or jewelry. Flush the affected area with water as soon as possible. Continue to irrigate until all of the contaminant is removed. |
Remove contact lenses. Irrigate immediately with water or saline for at least 15 minutes. If the eye is contaminated with solid particles, the eyelid should be completely everted and any solid material removed as quickly as possible while continuing to irrigate the eye. A topical anesthetic should be considered for all patients to enable the patient to open the lids sufficiently for effective irrigation. |
If, following irrigation, any of the following are apparent: Ocular pain (other than mild and resolving) Erythema (other than mild and resolving) Decreased visual acuity Ocular discharge/crusting A full ophthalmologic examination should be undertaken and any injury appropriately treated. |
ANTIDOTE(S)
There Are No Antidotes For This Substance |
There is no specific antidote for the treatment of this poisoning. Treatment is based on symptomatic and supportive care. |
ENHANCED ELIMINATION
Enhanced Elimination Not Recommended |
Hemodialysis or hemoperfusion may be indicated for secondary complications, such as acidosis or renal failure, but not for toxin removal alone. |
SUPPORTIVE CARE
Heart rate Blood pressure ECG (12 lead) Cardiac monitoring Respiratory function Blood gas analysis (if compromised respiratory function) Neurological status Serum electrolytes Renal function On-set of paralysis |
Gastrointestinal Irritation |
Due to nicotinic receptor over-stimulation gastrointestinal distress is common. Vomiting and diarrhea contribute to hypotension and fluid and electrolyte imbalances, potassium loss may increase the risk of cardiac dysrhythmia. Patients may require symptomatic care with antiemetic medication, IV fluids, and electrolyte replacement.  |
Observe patient for: Nausea Vomiting Abdominal pain Hematemesis Diarrhea Monitor: Blood pressure Fluid balance Serum electrolytes (if severe GI symptoms) Acid-base balance (if severe GI symptoms) |
Manage gastrointestinal irritation following standard treatment protocols. |
The sedation phase of hemlock toxicity can lead to reduced levels of consciousness and coma.  |
Closely monitor level of consciousness. |
Manage coma following standard treatment protocols. |
Seizures may develop after the ingestion of hemlock, though this has not been described in most case reports. Seizures should be treated with a benzodiazepine. |
Observe the patient closely for onset of seizure activity. |
The sedation phase of hemlock toxicity will cause weakness and paralysis, which includes muscle weakness. This can lead to respiratory arrest.  Intense respiratory support, when needed, constitutes the most vital supportive measure in preventing a poor outcome. Respiratory failure is usually the most common cause of death. |
Monitoring for respiratory failure should include: Chest auscultation Oxygen saturation Blood gas analysis |
Manage respiratory failure following standard treatment protocols. |
The late inhibitory phase of conium toxicity will result in bradycardia.  |
Monitor: Heart rate/rhythm Blood pressure ECG |
Manage bradycardia following standard treatment protocols. |
The toxic effect of conium may result in the paralysis of skeletal muscles, which may lead to rhabdomylosis;  this is characterized by an increase in muscle enzymes and the urine becoming red-brown, due to the presence of myoglobin. |
Examine patient for muscle tenderness/pain and weakness. Monitor: Serum creatine kinase (increased CK-MM isoenzyme) Urinalysis: Myoglobin pH |
Acute renal failure can occur as a result of rhabdomylosis. |
Patients should be monitored for the onset of acute kidney injury: Urine output Serum creatinine Blood urea nitrogen (urea) Proteinuria |
Manage acute kidney injury following standard treatment protocols. |
DISCHARGE CRITERIA
Patients may be discharged from hospital care when clearly asymptomatic and fully recovered from any complications. Appropriate psychiatric intervention may be necessary depending on the circumstances of the exposure. |
FOLLOW UP
Medical follow-up is unlikely to be required. Psychiatric intervention may be necessary depending on the circumstances of the exposure. |
PROGNOSIS
Following appropriate supportive care the prognosis is good. |
SIGNS AND SYMPTOMS
The effects of coniine are similar to those of nicotine, but with more pronounced CNS and curare-like actions. General signs are salivation, vomiting, dilation of the pupils, blurred vision, incoordination, myalgia, muscle fasciculations or flaccid paralysis, coldness of the extremities, and slow weak pulse. Subsequently the pulse may become rapid and thready followed by coma, convulsions, and eventually death from respiratory paralysis.   Rhabdomyolysis and subsequent renal failure have also been reported.  |
Systemic symptoms can occur after ingestion of fresh hemlock plant material; drying is thought to somewhat reduce toxicity, but poisonings have still occurred. Seeds of hemlock are toxic whether fresh or dried. Although the active alkaloids are oily volatile liquids, deaths have been reported after drinking liquid from boiling hemlock leaves.  Poisoning has also transpired from use of the hollow stem as a musical instrument or pea shooter.  Meat of birds, which eat hemlock seeds during migratory flights, is also poisonous to humans.  |
Onset/Duration of Symptoms |
Symptoms could be expected to appear quite promptly, due to rapid absorption and the onset of similar compounds such as nicotine. One report describes the onset of symptoms occurring within 30 minutes of eating hemlock leaves  whereas another case reports the death of a child 3 hours after ingesting plant leaves.  Effects usually persist for between 4 to 24 hours.   Animal studies have shown an onset of 0.5 to 2 hours with duration of 3 to 7 hours.   |
Mild Conium maculatum Toxicity | Moderate Conium maculatum Toxicity | Severe Conium maculatum Toxicity | GI effects Thirst Nausea Vomiting Agitation | Severe GI effects Salivation Abdominal pain Mydriasis Muscle weakness Muscle fasciculations Myalgia Drowsiness Tachycardia Tachypnea Respiratory depression | Bradycardia Hypotension Seizures Paralysis Rhabdomyolysis Renal failure Respiratory failure Coma |
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ACUTE EFFECTS (ROUTE OF EXPOSURE)
Local dermatitis (with or without blisters)  Burning sensation  Numbness  Systemic symptoms have not been reported following skin exposure. |
ACUTE EFFECTS (ORGAN SYSTEM)
Nausea   Vomiting   Hypersalivation   Thirst  Abdominal pain  |
Tremor   Dizziness   Nervousness  Agitation Headache  CNS depression  Ataxia  Dysarthria  Hypotonia  Hyperreflexia  Arreflexia  Absent oculocephalic reflex  Absent gag reflex  Muscle paralysis  Seizures  Coma   |
Tachypnea   Dyspnea  Hypoxia  Respiratory depression  Respiratory paralysis  |
Hypertension  Bradycardia   Widened QRS  Weak and thready pulse  Asystole  |
Muscle fasciculations  Myalgia  Muscle edema  Decreased muscle tone  Skeletal muscle paralysis  Rhabdomyolysis   |
Urination  Acute tubular necrosis   Renal failure (secondary to rhabdomyolysis)  |
Blurred/double vision   Amblyopia  |
Elevated INR  Prolonged partial thromboplastin time  |
Fever  |
TOXICITY
The toxic content of plants may vary from year to year due to various factors affecting their growth, such as available moisture and spring temperatures. Thus, it is difficult to establish an association between the severity of symptoms and the ingestion of a specific amount of plant material. |
HUMAN
The primary toxic effects of this plant are due to coniine, but the toxicity of this plant may vary considerable from that of its toxic component, due a number of different considerations, including toxic concentration, and growth factors of this plant.
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Poison hemlock has been responsible for many human fatalities because of the resemblance of the seed to Anise, the leaves to parsley or carrot, and the roots to parsnips.
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All parts, especially the seeds, should be regarded as poisonous, even when dried. An adult lethal dose is 100 to 300 mg of the toxic alkaloids.  This approximately corresponds to: Root 40 g in a 60 kg adult 10 g in a 15 kg child Shoots 29 to 1000 g in a 60 kg adult 7 to 250 g in a 15 kg child Leaves 13 to 67 g in a 60 kg adult 3 to 17 g in a 15 kg child Flowers 20 g in a 60 kg adult 5 g in a 15 kg child Unripe fruit 7 to 30 g in a 60 kg adult 2 to 8 g in a 15 kg child Ripe fruit 20 to 100 g in a 60 kg adult 5 to 25 g in a 15 kg child Seeds 22 to 100 g in a 60 kg adult 6 to 25 g in a 15 kg child |
Toxicity is likely to occur after any ingestion of this plant. |
142 g of Hemlock (ingested) Treatment unknown Fatal Hemlock leaves (ingested) 4 year male: cns depression developed after 30 minutes and was unrousable for 2 hours. Vomiting occurred Decontamination and supportive care, including gastric lavage, activated charcoal, dextrose, and nalorphine infusions Recovered and discharged after 2 days Unknown amount of Hemlock (ingested) 6 year female: burning sensation in the mouth, sialorrhea, tremor, and ataxia 2 hours post-ingestion. Agitation, loss of motor function, mydriasis, sinus tachycardia, elevated INR and increased PTT also occurred Decontamination and supportive care, including gastric lavage, activated charcoal, IV crystalloid infusion, and fresh frozen plasma Recovered and discharged after 3 days |
Two adults died after ingesting an unknown amount of hemlock, which was prepared by boiling the leaves in water. Adults have become poisoned after ingesting the meat from birds that have ingested hemlock buds. The birds themselves (robins, skylarks, chaffinches) were not susceptible to the alkaloids. |
Unknown amount of Hemlock (ingested) 19 year female: dizziness, headache, double vision, difficulty speaking, muscular weakness, dysarthria, and tachypnea on arrival. Dyspnea and hypoxia developed after 10 minutes after arrival Supportive care, including mechanical ventilation and intubation Recovered and discharged Unknown amount of cooked Hemlock (ingested) 45 year male: nausea, perioral numbness, dizziness, blurred vision, limb weakness, and bradycardia 1 hour post-ingestion Supportive care, including IV fluids and activated charcoal Recovered after 8 hours Unknown amount of cooked Hemlock (ingested) 45 year female: nausea, perioral numbness, dizziness, blurred vision, and limb weakness developed 1 hour post-ingestion. Respiratory arrest occurred soon after admission Supportive care, including intubation and mechanical ventilation Recovered and discharged after 4 days Unknown amount of ground up Hemlock with amitriptyline and diazepam (ingested) 28 year male: unresponsive with GCS of 3, fever, tachycardia, mild hypertension, tachypnea, mydriasis, decreased muscle tone, arreflexia, widened QRS on arrival. Absent oculocephalic reflex occurred on day 2. Developed hyperreflexia on day 6 Supportive care, including intubation, IV etomidate, rocuronium, and IV sodium bicarbonate Recovered after 14 days |
ANIMAL
LD50 Oral, Mouse | 12 mg/kg12 mg/kg/ |
LD50 Oral, Mouse | 100 mg/kg100 mg/kg/ |
LD50 Oral, Mouse | 204.5 mg/kg204.5 mg/kg/ |
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Birds Some small birds are not susceptible to coniine poisoning, consuming the seeds as a food source, and therefore may have the potential to cause toxicity in any species ingesting them. In contrast, deaths have resulted in other larger birds such as chickens and turkeys.   Farm Animals Severe poisoning and fatalities in cattle, goats, horses, sheep, and pigs have resulted from poison hemlock exposure. Symptoms generally involve movement problems, increased salivation and urination, tremor, vocalization, muscle weakness, and respiratory problems, all which can occur quite rapidly.    Other animals including rabbits and elk are affected in a similar way to farm animals. |
REPRODUCTION
PREGNANCY
It is unknown whether coniine crosses the placenta but poison hemlock is likely to affect the infant. Any exposure to poison hemlock should be avoided during pregnancy. No human information is available however Conium maculatum appears to act as a teratogen and abortifacient in animal poisonings. |
LACTATION
It is unknown if exposure to, or ingestion of, this plant results in excretion of toxic substances into breast milk. |
FERTILITY
It is unknown if exposure to, or ingestion of, this plant causes impaired fertility. |
TOXIC COMPONENTS
Piperazine plant alkaloids include: Conhydrine Coniine Gamma-Coniceine N-Methylconiine Pseudoconhydrine Coniine and gamma-coniceine are found in the largest amounts and combined account for most of the plant’s toxic activity. Coniine is about 8 times more toxic than gamma-coniceine.  These alkaloids are structurally related to nicotine, and could be expected to produce similar symptoms. |
All parts of the plant contain toxic piperidine alkaloids.
Before flowering, the leaves contain the most alkaloids, but the greatest concentrations are found in the flowers and fruits/seeds. The roots, at all times, contain the least.
Younger plants have 0.3 to 0.6% in leaves and 0.15% in other plant material (excluding flowers and fruit). Older plants contain approximately 1% in all parts of the plant. 
The alkaloid content, however, does vary with the climatic conditions. In good growing seasons, the average weight of the fruits and thus the quantity of alkaloids can be twice that of normal. Drying the plant reduces the alkaloid content.
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TOXIC MECHANISM
Coniine alkaloids affect the neurological junction where they act as non-depolarizing neuromuscular blockers, similar to curare. However, they also act on autonomic nervous system ganglia with varying degrees of stimulator, and inhibitor (biphasic) effects (resembling the effects of nicotine). |
BIOLOGICAL LEVELS - TOXIC
Coniine (or other plant alkaloids) blood levels are not readily available, nor necessary for clinical management.
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KINETICS
No human pharmacokinetic data were found in the literature. |
DESCRIPTION
PLANT ATTRIBUTES
Appear in almost flat-topped clusters of 2 mm white flowers. Each cluster is 2 to 5 cm in diameter.  |
The root is generally a thick yellow or white tap root (similar to a parsnip), which may or may not have branches.  |
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NZ: 23.May.2022 |