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Cicuta, commonly known as water hemlock, is a genus of four species of highly in the family Apiaceae. They are Perennial plant herbaceous plants which grow up to tall, having distinctive small green or white flowers arranged in an umbrella shape (umbel). Plants in this genus may also be referred to as cowbane or poison parsnip. Cicuta is native to temperate regions of the Northern Hemisphere, mainly North America and Europe, typically growing in , along streambanks and other wet and marshy areas. In the United Kingdom it is frequently found along canals. These plants bear a close resemblance to other members in the family Apiaceae and may be confused with a number of edible or poisonous plants. The common name hemlock may also be confused with poison hemlock ( Conium maculatum), or with the Hemlock tree.
Water hemlock is considered one of the most toxic plants in North America and Europe, being highly poisonous to humans. Three members of the genus contain a toxin named cicutoxin which causes central nervous system stimulatory effects including following ingestion. Medical treatment of poisoning may include the use of activated charcoal to decrease gastrointestinal absorption of the toxic principle along with supportive care including anticonvulsant drugs such as a benzodiazepine. High doses of anticonvulsant medicine are often required to halt seizure activity and further medical care including intubation and mechanical ventilation may be required.
| Cicuta bulbifera Carl Linnaeus | bulblet-bearing water hemlock, bulbous water hemlock |
| Cicuta douglasii (DC.) Thomas Coulter & Rose | Douglas water hemlock, western water hemlock |
| Cicuta maculata Carl Linnaeus | spotted cowbane, spotted parsley, spotted water hemlock |
| Cicuta virosa Carl Linnaeus | cowbane, Mackenzie's water hemlock, northern water hemlock |
Other species names such as Cicuta bolanderi, Cicuta californica, and Cicuta curtissii are older names now recognized to be varieties of the widespread, morphologically variable Cicuta maculata. Cicuta maculata is now recognized to have four varieties: var. maculata, var. angustifolia, var. victorinii, and var. bolanderi. Phylogenetics analysis using the sequences of nuclear ribosomal DNA internal transcribed spacer (ITS) loci was not conclusive but seems to show that C. bulbifera and C. virosa are monophyletic, while C. douglasii may not be. It was also suggested a specimen from California may warrant recognition as a distinct species. Other common names for the genus in general include poison parsnip, beaver poison, wild carrot, wild parsnip, and false parsley.
Additionally, there can be confusion between the various water hemlock species and poison hemlock ( Conium maculatum) as the common name hemlock is applied to both Cicuta and Conium maculatum. Both are poisonous and can be differentiated by differences in their root structure. Water hemlock has a branched root systems with tubules, while poison hemlock has a single tap root. Another reliable method to identify water hemlock is to examine the leaf veins. Water hemlock is unique in the family Apiaceae in that it has leaf veins which terminate in the notches between the leaf tips, rather than extend to the tip of the leaf, as is found in the leaf structure of other members of this family.
The in mice administered cicutoxin by intraperitoneal injection is 48.3 milligrams per kilogram body weight; this compares with 5.9 mg/kg for mice given potassium cyanide by intraperitoneal injection, while the LD50 for arsenic via intraperitoneal injection in mice is 46.2 mg/kg. The exact toxic dose of plant material in humans is unknown; it is thought ingestion of water hemlock in any quantity can result in poisoning, and very small amounts may lead to death. Poisoning has been reported following children blowing whistles made from the hollow stem of water hemlock plants. Intoxication has also been reported following skin contact with the plant; in one case, a family of five rubbed the plant onto the skin and were poisoned, with two children dying. Livestock have long been the worst affected, leading to the common name "cowbane". Poisoning in livestock is common and typically occurs following ingestion of roots of the plant. When the ground is soft in Spring, grazing animals tend to pull the entire plant out of the ground, ingesting both the foliage and the roots. Roots exposed by ploughing can also be the source of livestock poisonings. Ingestion of plant material may cause death in the animal in as little as 15 minutes.
Death is usually caused by respiratory failure or ventricular fibrillation secondary to ongoing seizure activity; fatalities have occurred within a few hours of ingestion. Poisoned people who recover usually regain consciousness and seizures cease within 24 to 48 hours of poisoning, although seizures may persist for up to 96 hours. There are occasional long-term effects, such as retrograde amnesia of the events leading to intoxication and the intoxication itself. Other ongoing mild effects may include anxiety, muscle weakness, Fasciculation, and anxiety. Complete resolution of symptoms may take a number of days, or these ongoing symptoms may persist for months after poisoning.
Initial treatment of poisoning may include gastrointestinal decontamination with activated charcoal. Decontamination is typically performed only if a potentially toxic amount of plant matter has been ingested up to one hour previously, and the patient has a normal intact airway or has been Intubation. There is no specific antidote for water hemlock poisoning, and treatment consists mainly of supportive care. Treatment may include control of with the administration of a such as lorazepam or diazepam, or, if seizures are refractory to this treatment, a barbiturate such as phenobarbital is administered. The anticonvulsant phenytoin is not recommended, as it has not been shown to be effective for seizure control following water hemlock poisoning. Treatment with high doses of benzodiazepines or barbiturates may cause respiratory depression, and respiratory support including intubation and mechanical ventilation is required in these patients. Continuous electroencephalography monitoring is recommended in symptomatic patients.
Further treatment for complications of metabolic acidosis, rhabdomyolysis, hyperthermia, or low blood pressure may be required. Metabolic acidosis is treated by administering sodium bicarbonate. Low blood pressure is usually treated with intravenous fluid replacement, but the administration of dopamine or norepinephrine may be required to restore blood pressure. The management of rhabdomyolysis includes ensuring adequate hydration and urinary alkalinization; a complication of rhabdomyolysis is acute kidney injury, which may require management with hemodialysis. However, hemodialysis, hemoperfusion, or other extracorporeal techniques do not remove cicutoxin from the blood and are therefore not useful in enhancing elimination.
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