Pesticides, Metals, and Environmental Toxicology
Cholinesterase inhibitors
Organophosphates and carbamates produce a cholinergic syndrome (SLUDGE/DUMBELS): salivation, lacrimation, urination, diarrhea, bronchorrhea, broncho/pradycardia, miosis, and muscle fasciculations. Atropine is titrated until secretions dry - the pupil and heart rate are unreliable endpoints. Pralidoxime reactivates the enzyme before "aging" and is most useful in organophosphate (not carbamate) poisoning. Complications include intermediate syndrome (24–96 hours) and delayed polyneuropathy.
Other pesticides
Pyrethroids cause sodium-channel prolongation with paresthesias and tremor; there is no specific antidote. Paraquat ingestion is often fatal via oxidative lung injury - give supplemental oxygen only for documented hypoxemia, because oxygen accelerates pulmonary fibrosis.
Metals
- Lead: chelate children above roughly 45 µg/dL (succimer) and use dimercaprol plus calcium disodium EDTA in encephalopathy. Never give succimer alone in encephalopathy.
- Iron: deferoxamine; look for metabolic acidosis, GI symptoms, and a high anion gap.
- Arsenic: dimercaprol or succimer. Mercury: dimercaprol for inorganic salts. Thallium: Prussian blue. Copper: penicillamine or trientine.
Environmental concepts
Bioaccumulation, biomagnification, and persistence explain why methylmercury magnifies up the food chain (Minamata disease), and cadmium causes Itai-itai disease with renal tubular and bone injury.
Rule of thumb: a patient with pinpoint pupils, bronchorrhea, and fasciculations has cholinergic poisoning until proven otherwise - give atropine and oxygen before searching for the pesticide container.