Review Question - QID 214907

This patient who presents with nausea, vomiting, diarrhea, hypotension, bradycardia, miosis, and wheezing is most likely suffering from organophosphate poisoning secondary to insecticide exposure. The treatment for organophosphate exposure is atropine and pralidoxime.

Organophosphates are organic compounds that are used as herbicides, insecticides, and chemical warfare weapons. Organophosphates irreversibly inhibit acetylcholinesterase and block the metabolism of acetylcholine, resulting in increased acetylcholine activity. The symptoms associated with this increase in acetylcholine are largely parasympathetic in nature and can be remembered with the acronym DUMBBELSS (Diarrhea, Urination, Miosis, Bronchospasm, Bradycardia, Excitation of systems, Lacrimation, Sweating, and Salivation). Treatment of organophosphate poisoning include atropine, which competitively inhibits muscarinic acetylcholine receptors, and pralidoxime, which detaches the poison from acetylcholinesterase enzymes and reactivates it. Atropine should be given first to all patients with organophosphate poisoning followed by pralidoxime.

Incorrect Answers:
Answer 1: Ammonium chloride is the antidote for amphetamine poisoning because it acidifies the urine and promotes urinary excretion of amphetamines. Amphetamine poisoning would present with agitation, tremors, delirium, hypertension, and tachycardia.

Answer 2: Antivenom is the antidote for rattlesnake bites, which may also present with nausea, vomiting, hypotension, and sweating in a farm laborer. The additional constellation of symptoms including miosis and wheezing as well as the absence of a bite wound or history of bite makes organophosphate exposure more likely.

Answer 3: Naloxone is the antidote for opioid overdose, which may also present with pinpoint pupils and bradycardia; however, the additional antimuscarinic symptoms such as diarrhea, vomiting, and wheezing are more consistent with organophosphate poisoning.

Answer 4: Physostigmine is an acetylcholinesterase inhibitor that can be used to treat patients who overdose on drugs with anticholinergic effects such as atropine. Physostigmine would make organophosphate poisoning worse because it acts through the same mechanism.

Bullet Summary:
A patient with organophosphate poisoning should be first given the muscarinic acetylcholine receptor antagonist atropine followed by pralidoxime, which functions by detaching the poison from acetylcholinesterase.