The correct answer is A. The child is exhibiting symptoms of excessive parasympathetic tone after exposure to an unknown substance. This is a classic case of severe organophosphate poisoning. Symptoms include lacrimation, salivation, blurred vision, urinary incontinence, diarrhea, and diaphoresis. Other more severe effects are bronchospasm, bradycardia, hypotension, respiratory paralysis, and mental status change. Organophosphates include many pesticides that irreversibly react with postsynaptic acetylcholinesterase molecules and inhibit their activity. Atropine is the drug of choice to treat the acute toxic effects of organophosphate poisoning by blocking muscarinic acetylcholine receptors. In addition, an antidote, pralidoxime, can reactivate acetylcholinesterases bound by organophosphates and should be administered along with atropine.
The bronchospasm and hypotension arises from increased cholinergic activity not from an inflammatory or anaphylactic response. Corticosteroids (choice B) are not useful in this situation.
Edrophonium (choice C) is an inhibitor of acetylcholinesterase and has effects similar to organophosphates, so it would only worsen his symptoms.
Epinephrine (choice D) may improve the bronchospasm, bradycardia, and hypotension, but it will counteract the other effects of organophosphate poisoning.
Methylene blue (choice E) is the antidote for severe methemoglobinemia. It is not indicated in organophosphate poisoning.
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