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Toxicology – Carbamate Poisoning
Sources
Carbamates are commonly found in insecticides such as carbaryl, aldicarb, carbofuran, and methomyl. They are also present in certain medications, including acetylcholinesterase inhibitors used for Alzheimer disease (e.g., rivastigmine) and therapeutic agents like neostigmine and physostigmine.
Typical Presentation
A common scenario involves accidental or intentional ingestion, particularly in children exposed to insecticides. Patients typically present with features of a cholinergic toxidrome, including excessive secretions, altered mental status, and respiratory symptoms.
Mechanism of Action
Carbamates inhibit acetylcholinesterase at synapses in both the central and peripheral nervous systems, as well as in red blood cells. Unlike organophosphates, this inhibition is reversible because carbamates do not cause “aging” of the enzyme, making their toxicity generally less severe.
Clinical Features
Muscarinic symptoms predominate and include miosis, bradycardia, salivation, sweating, bronchorrhea, bronchospasm, nausea, vomiting, diarrhea, lacrimation, and urinary incontinence. Central nervous system effects include confusion, lethargy, coma, and seizures. Nicotinic effects include muscle fasciculations and weakness. Severe cases may lead to death.
Management
Treatment involves prompt decontamination and supportive care. Atropine is administered to control muscarinic symptoms, particularly respiratory secretions, starting at 2–5 mg IV in adults (0.05 mg/kg in children) and repeated every 3–5 minutes with dose escalation until improvement is achieved. Pralidoxime may be used for neuromuscular symptoms, although its role is less critical compared to organophosphate poisoning. Benzodiazepines are indicated for agitation, muscle spasms, and seizures. Autoinjectors containing atropine and pralidoxime are available for emergency use.
Key Points
Sources
Carbamates are commonly found in insecticides such as carbaryl, aldicarb, carbofuran, and methomyl. They are also present in certain medications, including acetylcholinesterase inhibitors used for Alzheimer disease (e.g., rivastigmine) and therapeutic agents like neostigmine and physostigmine.
Typical Presentation
A common scenario involves accidental or intentional ingestion, particularly in children exposed to insecticides. Patients typically present with features of a cholinergic toxidrome, including excessive secretions, altered mental status, and respiratory symptoms.
Mechanism of Action
Carbamates inhibit acetylcholinesterase at synapses in both the central and peripheral nervous systems, as well as in red blood cells. Unlike organophosphates, this inhibition is reversible because carbamates do not cause “aging” of the enzyme, making their toxicity generally less severe.
Clinical Features
Muscarinic symptoms predominate and include miosis, bradycardia, salivation, sweating, bronchorrhea, bronchospasm, nausea, vomiting, diarrhea, lacrimation, and urinary incontinence. Central nervous system effects include confusion, lethargy, coma, and seizures. Nicotinic effects include muscle fasciculations and weakness. Severe cases may lead to death.
Management
Treatment involves prompt decontamination and supportive care. Atropine is administered to control muscarinic symptoms, particularly respiratory secretions, starting at 2–5 mg IV in adults (0.05 mg/kg in children) and repeated every 3–5 minutes with dose escalation until improvement is achieved. Pralidoxime may be used for neuromuscular symptoms, although its role is less critical compared to organophosphate poisoning. Benzodiazepines are indicated for agitation, muscle spasms, and seizures. Autoinjectors containing atropine and pralidoxime are available for emergency use.
Key Points
- Carbamates cause reversible inhibition of acetylcholinesterase and are generally less toxic than organophosphates.
- Central-acting acetylcholinesterase inhibitors such as donepezil and tacrine, used in Alzheimer disease, can produce cholinergic toxicity in overdose.
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