FPGEE Toxicology 2 — Questions and Answers
Question 1: Which antidote is used to treat cyanide poisoning by acting as a methemoglobin-forming agent?
- Sodium thiosulfate alone
- Amyl nitrite followed by sodium nitrite (Correct answer)
- Hydroxocobalamin only
- Dimercaprol
Correct answer: Amyl nitrite followed by sodium nitrite
Amyl nitrite and sodium nitrite generate methemoglobin, which competes with cytochrome oxidase for cyanide, while sodium thiosulfate converts cyanide to thiocyanate.
Question 2: A patient presents with miosis, bradycardia, excessive secretions, and muscle fasciculations after a suspected pesticide exposure. What is the most likely toxidrome?
- Sympathomimetic
- Anticholinergic
- Cholinergic (Correct answer)
- Opioid
Correct answer: Cholinergic
Organophosphate or carbamate pesticides inhibit acetylcholinesterase, causing a cholinergic toxidrome with SLUDGE/DUMBELS symptoms including miosis, bradycardia, and secretions.
Question 3: The Rumack-Matthew nomogram is used to guide treatment decisions in which type of poisoning?
- Salicylate overdose
- Acetaminophen overdose (Correct answer)
- Iron overdose
- Lithium toxicity
Correct answer: Acetaminophen overdose
The Rumack-Matthew nomogram plots serum acetaminophen concentration against time post-ingestion to predict hepatotoxicity risk and the need for N-acetylcysteine.
Question 4: Which heavy metal toxicity is classically associated with Mees' lines on fingernails, peripheral neuropathy, and garlic odor on the breath?
- Lead
- Mercury
- Arsenic (Correct answer)
- Thallium
Correct answer: Arsenic
Chronic arsenic poisoning causes Mees' lines (transverse white lines on nails), peripheral neuropathy, and a characteristic garlic-like breath odor.
Question 5: What is the mechanism by which iron causes toxicity in overdose?
- Inhibition of acetylcholinesterase
- Free radical generation via the Fenton reaction (Correct answer)
- Competitive antagonism of vitamin K
- Blockade of sodium channels
Correct answer: Free radical generation via the Fenton reaction
Excess iron catalyzes the Fenton reaction, converting hydrogen peroxide to hydroxyl radicals that cause lipid peroxidation and mitochondrial dysfunction.
Question 6: A patient takes an overdose of a tricyclic antidepressant. Which ECG finding is most predictive of life-threatening arrhythmias?
- Prolonged QTc interval
- QRS duration greater than 100 ms (Correct answer)
- ST-segment depression
- T-wave inversion in V1-V4
Correct answer: QRS duration greater than 100 ms
QRS prolongation greater than 100 ms due to sodium channel blockade by tricyclic antidepressants predicts ventricular arrhythmias and seizures.
Question 7: Which chelating agent is the treatment of choice for acute lead encephalopathy in children?
- Dimercaprol (BAL) plus EDTA (Correct answer)
- Penicillamine alone
- Succimer (DMSA) alone
- Deferoxamine
Correct answer: Dimercaprol (BAL) plus EDTA
BAL is given first to mobilize lead, followed by EDTA; this combination is preferred in severe lead toxicity with encephalopathy to prevent further CNS deposition.
FPGEE Toxicology 2
Which antidote is used to treat cyanide poisoning by acting as a methemoglobin-forming agent?