FPGEE Toxicology 4 — Questions and Answers
Question 1: A patient presents with altered mental status, hyperthermia, diaphoresis, and hyperreflexia after starting linezolid while already on sertraline. What is the most likely diagnosis?
- Neuroleptic malignant syndrome
- Anticholinergic toxidrome
- Serotonin syndrome (Correct answer)
- Malignant hyperthermia
Correct answer: Serotonin syndrome
Linezolid is an MAO inhibitor; combined with an SSRI it causes excess serotonin activity resulting in serotonin syndrome characterized by hyperthermia, clonus, and agitation.
Question 2: The LD50 is a toxicological parameter that represents:
- The dose that produces toxic effects in 50% of animals
- The lethal dose for 50% of a test animal population (Correct answer)
- The dose that causes liver damage in 50% of subjects
- The dose that saturates drug metabolism in 50% of subjects
Correct answer: The lethal dose for 50% of a test animal population
LD50 (median lethal dose) is the dose of a substance required to kill 50% of the test population under specific experimental conditions, used to compare acute toxicity.
Question 3: Which of the following correctly describes zero-order (saturation) toxicokinetics?
- A constant fraction of drug is eliminated per unit time
- A constant amount of drug is eliminated per unit time (Correct answer)
- Elimination rate increases proportionally with concentration
- Half-life decreases as concentration increases
Correct answer: A constant amount of drug is eliminated per unit time
Zero-order kinetics occur when elimination pathways are saturated; a fixed amount (not fraction) is eliminated per unit time, leading to disproportionate increases in drug levels with dose increases.
Question 4: A child ingests iron tablets. During the latent phase (6-24 hours post-ingestion), the patient appears to improve. What dangerous misconception can this create?
- The ingested iron has been fully absorbed
- The false sense of recovery may delay needed treatment before systemic toxicity begins (Correct answer)
- Hepatic failure has already resolved
- The iron has been converted to non-toxic ferritin
Correct answer: The false sense of recovery may delay needed treatment before systemic toxicity begins
The latent phase of iron poisoning creates a deceptive improvement after initial GI symptoms, but systemic toxicity, hepatic failure, and circulatory collapse may follow without treatment.
Question 5: Which of the following correctly pairs a toxin with its specific antidote?
- Heparin — protamine sulfate (Correct answer)
- Warfarin — phytonadione (vitamin K1) — no additional antidote exists
- Benzodiazepines — naloxone
- Beta-blockers — atropine as sole treatment
Correct answer: Heparin — protamine sulfate
Protamine sulfate neutralizes heparin by forming an inactive complex; it is the specific antidote for heparin-induced anticoagulation.
Question 6: In organophosphate poisoning, pralidoxime (2-PAM) must be given early because:
- It reverses muscarinic effects better than atropine
- Aged cholinesterase cannot be reactivated by pralidoxime (Correct answer)
- It has a shorter half-life than atropine
- It prevents metabolism of organophosphates to active metabolites
Correct answer: Aged cholinesterase cannot be reactivated by pralidoxime
The organophosphate-enzyme complex undergoes 'aging' (permanent covalent bonding) over time; once aged, pralidoxime cannot regenerate acetylcholinesterase activity.
Question 7: A patient develops methemoglobinemia after topical benzocaine use. Which finding confirms the diagnosis?
- PaO2 of 45 mmHg on ABG with normal pulse oximetry
- Co-oximetry showing elevated methemoglobin fraction with normal or high PaO2 (Correct answer)
- Pulse oximetry reading of 85% with SpO2 saturation gap on ABG
- Serum carboxyhemoglobin level of 30%
Correct answer: Co-oximetry showing elevated methemoglobin fraction with normal or high PaO2
Co-oximetry directly measures methemoglobin; PaO2 is typically normal because dissolved oxygen is unaffected, but hemoglobin cannot carry or release oxygen effectively.
FPGEE Toxicology 4
A patient presents with altered mental status, hyperthermia, diaphoresis, and hyperreflexia after starting linezolid while already on sertraline.
What is the most likely diagnosis?