What is Carbamate Toxicity?
Carbamates are a type of bug spray that works in a similar way as another type of insecticide called organophosphates (OP). They are chemicals made from a substance called carbamic acid and they work by modifying a protein in nerve cells called acetylcholinesterase. This protein plays a key role in sending messages between nerve cells and muscle cells.
Just like organophosphates, carbamates also bind to acetylcholinesterase, but they do so in a way that can be reversed. Because of their similar mechanisms, poisoning from carbamates can look a lot like poisoning from organophosphates. However, the harmful effects of carbamates usually last less than a day.
Some common types of carbamates that can cause toxic exposure include aldicarb, carbofuran, carbaryl, ethinenocarb, fenobucarb, oxamyl, methomyl, pirimicarb, propoxur, and trimethacarb.
What Causes Carbamate Toxicity?
Getting exposed to carbamates, a toxic substance, can happen through skin contact, inhalation, or ingestion. According to the World Health Organization, pesticides are divided into five groups based on how lethal they are to rats when ingested. The severity of symptoms depends on the type of pesticide and the amount that has been exposed.
Most cases of carbamate poisoning happen because of purposeful oral ingestion or exposure through the skin in work environments. In developing countries, there have been instances of large outbreaks due to contaminated food and crops. Depending on the specific type of carbamates one gets exposed to, symptoms can show up quickly after skin exposure. Exposure can also happen from a combination of skin and inhalation exposure after working in areas recently sprayed or fogged with insecticides. There have been reported cases in children who played on a sports field after it had been sprayed with insecticides.
Risk Factors and Frequency for Carbamate Toxicity
From 2002 to 2006, data collected by the American Association of Poison Control Centers (AAPCC) found around 14,000 reported incidents of carbamate poisonings, with a death rate of 10 to 20%. In 2008, 8,000 cases were reported in the United States, leading to 14 deaths.
In less developed parts of the world, the lack of regulations for pesticides allows them to be used in farming, making it easier for people to unintentionally be exposed to harmful substances. In rural Asia, these substances are sometimes used for self-harm, leading to around 200,000 fatalities per year. It is estimated that these substances are used in 1 to 2 million cases annually in rural Asia. Of these, about 20 to 30% might develop respiratory failure.
- Work in these settings might result in severe exposure to carbamate and organophosphates.
- These chemicals are sometimes even used for intentional self-harm.
- These two types of insecticides require 1 to 2 million days of using ventilators every year globally.
- Therefore, they contribute significantly to worldwide illness, death, and medical costs.
Signs and Symptoms of Carbamate Toxicity
Carbamate toxicity, a type of poisoning, is often suspected due to specific signs and patterns of patient symptoms, known as a clinical toxidrome. This suspicion is vital because patients with central nervous system toxicity might be confused or less aware, making them unable to give a full medical history. Treatment for carbamate and another type of poisoning, organophosphate (OP) toxicity, is usually the same at the start since the signs of poisoning are very alike.
People who think it was an accidental exposure or an intentional ingestion of poison can help doctors identify the exact insecticide involved by using a Material Safety and Data Sheet. This information can be useful for making treatment decisions, particularly regarding a drug called pralidoxime.
A diagnosis of carbamate toxicity can be supported by symptoms such as excessive salivation, tear production, digestive problems, fluid in the bronchial tubes (bronchorrhea), and sweating. Heart rate can be either unusually slow or fast, and the pupils of the eyes can be either tiny or dilated because of the overstimulation of both the calming (parasympathetic) and the fight-or-flight (sympathetic) nervous systems.
Both OP and carbamate toxicity should be considered if someone comes in with pinpoint pupils, excessive sweating, and difficulty breathing. Long term, this poisoning may lead to permanent damage of the nerves, a condition known as chronic neuropathy.
Testing for Carbamate Toxicity
In cases of suspected carbamate poisoning, waiting for laboratory test results may potentially delay vital treatments. Indeed, the patient’s symptoms may begin to improve before the results come in. The tests usually measure the levels of butyrylcholinesterase (BuChE) and red cell acetylcholinesterase (RBC AChE).
BuChE is a substance generated in the liver and spilled into the blood, while RBC AChE is found in neuron connections. In cases of carbamate poisoning, RBC AChE levels usually return to normal quite swiftly. However, RBC AChE levels can show up erroneously low in severe cases if the test isn’t performed quickly enough or if the sample is not cooled or frozen immediately.
BuChE results can be challenging to understand due to widespread fluctuations in the average levels. Gauging them is tricky without knowing the patient’s typical or ‘baseline’ levels.
Treatment Options for Carbamate Toxicity
Carbamate pesticide exposure can lead to continuous absorption of the toxin through the skin. If this happens, it’s crucial to wash the skin as soon as possible. Medical providers should protect themselves from exposure by wearing protective gear, such as Neoprene or nitrile gloves, a gown, mask, and face shield. The exposed skin of patients needs to be thoroughly washed three times: once with water, once with soap and water, and then rinsed with water again. If someone accidentally swallows a high dose of carbamate pesticides, stomach washing might be necessary. However, this should only be done if the patient hasn’t vomited, the incident took place within an hour, and the patient has control over their airway. As carbamate pesticides can cause fits, breathing problems, and unconsciousness in extreme cases, a patient’s airways must be secured before their stomachs are washed.
When a person is poisoned by a carbamate pesticide, the biggest danger is the failure of the respiratory system, which can be fatal. This danger comes from bronchorrhea (excessive mucus in the air passages), weakness of the muscles (possibly leading to complete paralysis), and depression of the part of the brain that controls breathing. Medical attention should focus on ensuring good oxygen flow and stable breathing. An overabundance of respiratory secretions can be treated with a drug called atropine. This drug blocks the effects of excessive stimulation of the muscarinic receptors in the lung area. If patients struggle to manage their respiratory processes or show signs of mental disturbance or significant muscle weakness, a breathing tube should be inserted into their windpipe. In such instances, muscle relaxation should be achieved using non-depolarizing neuromuscular blockers such as rocuronium –rather than depolarizing ones like succinylcholine– to prevent an extended period of full-body paralysis.
Atropine can also help with other symptoms caused by an increase in acetylcholine levels. These symptoms include increased salivation and tear production, contraction of the pupil, vomiting, diarrhea, excessive sweating, urinary incontinence, and bronchial spasms. Atropine is generally given intravenously, with the dose being increased every five minutes until the symptoms improve. The right dose of atropine should help reduce bronchial secretions, bronchial restriction while improving blood pressure. If a person suffers from carbamate poisoning, they can also be given benzodiazepines for seizures and agitation if intubated. Lastly, for such patients, a suitable course of action would be continuous scrutiny of their respiratory condition in a monitored setting.
What else can Carbamate Toxicity be?
When dealing with a case of cholinesterase poisoning, doctors look into three types of cholinergic toxicity. They are:
- Cholinesterase inhibitors
- Cholinomimetics
- Nicotine alkaloids
Cholinesterase inhibitors include both insecticides like carbamates and organophosphates, and non-insecticides like pyridostigmine, physostigmine, neostigmine, and echothiophate. Among the non-insecticidal cholinesterase inhibitors, toxicity usually comes from consuming too much pyridostigmine, which is used to treat a muscle weakness disorder called myasthenia gravis. It’s less common to see toxicity from cholinesterase inhibitors used to treat Alzheimer’s disease, like donepezil.
Cholinomimetics either directly stimulate the receptors without inhibiting a certain enzyme called AChE. Laboratory tests will show normal levels of two types of AChE in these cases. Exposure to these compounds can come from medications like carbachol, methacholine, and pilocarpine, or certain types of mushrooms that contain a substance called muscarine.
Nicotine alkaloids, like nicotine and coniine, cause symptoms similar to carbamate toxicity, like increased activity in the central nervous system, autonomic activation, and skeletal muscle stimulation. These symptoms are the result of stimulation of the parasympathetic and sympathetic nervous systems and the nicotinic receptors on skeletal muscle.
What to expect with Carbamate Toxicity
Research into the initial evaluation of patient harm and possibility of death due to exposure to certain substances is limited. Information is typically pooled together for exposures to pesticides known as carbamates and organophosphates. Since the effects of carbamate exposure tend to last shorter, data on death rates, artificial ventilation periods, and healthcare costs are probably more reflective of organophosphate poisonings.
In a study observing patients recently poisoned with either organophosphates or carbamates, it was found that a low score on the Glasgow Coma Scale (a tool used to assess how severe a possible brain injury is) upon arrival at the hospital could predict a worse outcome. Specifically, exposure to a certain type of carbamate called ‘methomyl’ is linked to a high risk of the heart stopping when the patient first arrives at the hospital.
