Organophosphate Poisoning

Mechanism and exposure

Organophosphates are found in agricultural pesticides, some household insecticide sprays, and occupational chemical settings. They inhibit acetylcholinesterase, the enzyme that normally breaks down acetylcholine at synapses. The organophosphate binds the enzyme's active site and phosphorylates it, and unlike a simple reversible block, this bond strengthens over time through a process called aging, where the enzyme-toxin complex rearranges into a form no drug can reactivate. Once aging occurs, the body must manufacture entirely new enzyme, which takes time the patient may not have. This is why early treatment matters: the window to pharmacologically reactivate the enzyme is real but closing.

With acetylcholinesterase disabled, acetylcholine accumulates everywhere it acts: muscarinic receptors in glands and smooth muscle, nicotinic receptors at the neuromuscular junction and autonomic ganglia, and receptors throughout the central nervous system.

Recognizing the toxidrome

The muscarinic effects are taught with the mnemonics SLUDGE (salivation, lacrimation, urination, defecation, gastrointestinal distress, emesis) and DUMBELS (defecation, urination, miosis, bradycardia, bronchorrhea/bronchospasm, emesis, lacrimation, salivation). These are useful for exams, but the features that actually kill patients are the "killer B's": bronchorrhea (secretions flooding the airway), bronchospasm (constricted airways), and bradycardia. A patient can look like textbook SLUDGE and still die of respiratory failure from drowning in their own secretions.

Nicotinic effects appear as muscle fasciculations, generalized weakness, and eventually flaccid paralysis, including of the diaphragm. Central nervous system effects include agitation, confusion, seizures, and coma. A complete assessment tracks muscarinic, nicotinic, and central findings together, since treatment addresses each differently.

Priority-ordered management

Rescuer safety comes first. Organophosphates on a patient's skin, hair, or clothing can transfer to responders and cause secondary contamination, so appropriate personal protective equipment is mandatory before contact.

Decontamination follows immediately: remove and bag all clothing, and wash the skin thoroughly to stop ongoing absorption. Skipping this step lets exposure continue no matter what antidotes are given.

Airway and oxygenation come next. Secretions and bronchospasm can rapidly obstruct the airway, so suctioning and supplemental oxygen are often needed before or alongside drug therapy. If intubation is required, succinylcholine is problematic because it is metabolized by the same enzyme system disrupted by the poisoning, leading to unpredictably prolonged paralysis; a nondepolarizing alternative is generally preferred.

Atropine is the first-line antidote for the muscarinic effects. It is titrated not to a target heart rate but to drying of pulmonary secretions and easier ventilation, since the goal is clearing the airway, not "normalizing" vitals. Doses are escalated as needed, sometimes to amounts far larger than typical anticholinergic use, because massive acetylcholine excess requires massive antagonism.

Pralidoxime (an oxime) works differently: it reactivates acetylcholinesterase itself, addressing the nicotinic weakness and paralysis that atropine cannot touch. It is most effective when given before aging occurs, reinforcing the urgency of early recognition.

Benzodiazepines control seizures and agitation from central cholinergic overload; they are supportive rather than antidotal but are an essential part of stabilization.

Monitoring for delayed complications

Beyond the acute crisis, clinicians watch for intermediate syndrome, a period of proximal muscle weakness and possible respiratory compromise appearing after the acute toxidrome resolves, and for organophosphate-induced delayed neuropathy, a distinct nerve injury that can appear weeks later. Carbamate insecticides cause a related but reversible cholinesterase inhibition, since the carbamate-enzyme bond spontaneously breaks down without aging, generally producing a shorter, less severe course.