Organophosphates and carbamates are groups of related chemicals commonly used as pesticides to control insects. Some preparations are approved for veterinary use to control fleas and other parasites. They are commonly formulated as dusts, granules, emulsions, suspensions, or solutions. Concentrates are often formulated in a petroleum distillate base.
Clinically, poisonings from organophosphates and carbamates are similar to each other, resulting in the inhibition of acetylcholinesterase, causing stimulation of muscarinic and nicotinic receptors. Carbamate toxicity is generally of shorter duration as its effect on acetylcholinesterase is reversible.
Deaths from these products occur as a result of acute respiratory failure.
Attempt to identify the name and amount of the substance the patient was exposed to, including the pesticide control number, WHMIS information, or photo of the label. This can be relayed to CliniCall for additional information.
Health care staff, including paramedics and EMRs/FRs, should wear protective clothing when handling contaminated clothing and grossly contaminated patients.
Treatment should be directed at decontamination, administration of antidotes where available, and support for oxygenation and ventilation.
Carbamates include: bendiocarb; carbaryl; carbofuran; formetanate; methomyl; oxamyl; and propoxur.
Products may be labeled as “systemic” or “contact” – this refers to the action of the pesticide and whether it is taken into plant tissues. It has no bearing on human toxicity.
The onset of symptoms is usually within minutes to hours after exposure. Symptoms may be delayed in the case of skin exposure.
Symptoms can be divided into muscarinic effects (miosis, excessive sweating and bronchial secretions, bradycardia, hypotension) and nicotinic effects (mydriasis, tachycardia, fasciculations, muscle weakness, paralysis). Central nervous system effects can include headache, drowsiness, seizures, and unconsciousness.
Muscarinic receptors are predominantly in the parasympathetic nervous system whereas nicotinic receptors are primarily in the sympathetic nervous system.
A useful mnemonic for organophosphate toxicity is SLUDGEM/BBB:
The three “Bs” – bronchorrhea, bronchospasm, and bradycardia – are the most common causes of death in organophosphate and carbamate poisoning.
First Responder (FR) Interventions
Maintain a safe working environment:
Decontaminate as per CliniCall, fire department, or hazardous materials specialist on scene
Double the dose every five minutes until effect is seen
The goal is to control secretions and correction of significant bradycardia and hypotension; secretions respond more slowly than bradycardia
Atropine will reverse muscarinic symptoms but will not alter nicotinic effects
Critical Care Paramedic (CCP) Interventions
Intubate if necessary
Provide mechanical ventilation as required
Consider obtaining pralidoxime from a hospital while en route to call:
Do not administer pralidoxime without concurrently giving atropine
Loading dose: 1 – 2 g IV infused over 30 minutes
May be given by direct IV injection over 5 minutes in severely poisoned patients
First dose may be given IM if IV access is not possible
Maintenance dose: continuous infusions preferred; optimal dose not established; 500 mg/hr is often recommended; consider 8-10 mg/kg/hr (as per WHO guidance); lower rates may be adequate; titrate to response
Loading dose: 20-50 mg/kg
May also be given by direct IV injection over 5 minutes, or IM if IV access cannot be obtained
Maintenance dose: 10-20 mg/kg/hr
Therapeutic endpoint: control of nicotinic symptoms
Treatment for 24-48 hours is usually sufficient in many cases; prolonged treatment (i.e., several weeks) may be required in severe poisoning
Discontinue when patients no longer require ventilatory support
Pralidoxime use in carbamate poisoning is controversial; indicated for use in mixed organophosphate/carbamate poisoning
Risk of serious adverse effects (laryngospasm, hypertension) increases with rapid IV administration
May precipitate myasthenic crisis in patients with myasthenia gravis; may cause toxicity of carbaryl, a carbamate insecticide
May consider glycopyrrolate for organophosphate symptoms if atropine is ineffective or unavailable