NBME Pharmacology 3 — Questions and Answers
Question 1: A patient receives succinylcholine for rapid sequence intubation. Which condition represents an absolute contraindication to its use?
- Hypertension
- Crush injury 5 days ago (Correct answer)
- Renal failure
- Obesity
Correct answer: Crush injury 5 days ago
Denervation injuries or crush injuries cause upregulation of extrajunctional acetylcholine receptors; succinylcholine causes massive K+ efflux leading to fatal hyperkalemia.
Question 2: Which opioid analgesic is most appropriate for a patient with severe renal impairment requiring chronic pain management?
- Morphine
- Codeine
- Fentanyl (Correct answer)
- Hydromorphone
Correct answer: Fentanyl
Fentanyl is the preferred opioid in renal failure because it has no active metabolites that accumulate; morphine-6-glucuronide accumulates and causes toxicity in renal impairment.
Question 3: Methotrexate kills cancer cells primarily by inhibiting which enzyme?
- Thymidylate synthase
- Dihydrofolate reductase (Correct answer)
- Ribonucleotide reductase
- Topoisomerase II
Correct answer: Dihydrofolate reductase
Methotrexate competitively inhibits dihydrofolate reductase (DHFR), depleting tetrahydrofolate and blocking purine and thymidylate synthesis.
Question 4: A patient receiving cyclophosphamide for lymphoma develops painless hematuria. Which complication is occurring?
- Renal tubular necrosis from direct toxicity
- Hemorrhagic cystitis from acrolein metabolite (Correct answer)
- IgA nephropathy from immune activation
- Bladder wall ischemia from vasospasm
Correct answer: Hemorrhagic cystitis from acrolein metabolite
Cyclophosphamide is metabolized to acrolein, which accumulates in urine and causes direct urothelial damage resulting in hemorrhagic cystitis.
Question 5: Atropine is administered to reverse the effects of organophosphate poisoning. Which toxic effect of organophosphates does atropine NOT reverse?
- Bradycardia
- Bronchospasm
- Excessive secretions
- Skeletal muscle paralysis (Correct answer)
Correct answer: Skeletal muscle paralysis
Atropine blocks muscarinic receptors but has no effect on nicotinic receptors at the neuromuscular junction; pralidoxime (2-PAM) must be used to reverse skeletal muscle effects.
Question 6: A surgeon needs to provide postoperative analgesia while minimizing opioid use. Which mechanism do NSAIDs use to reduce pain and inflammation?
- Block sodium channels in sensory neurons
- Inhibit cyclooxygenase, reducing prostaglandin synthesis (Correct answer)
- Block histamine H1 receptors peripherally
- Activate GABA-A receptors in the spinal cord
Correct answer: Inhibit cyclooxygenase, reducing prostaglandin synthesis
NSAIDs inhibit COX-1 and COX-2 enzymes, preventing arachidonic acid conversion to prostaglandins that sensitize pain receptors and mediate inflammation.
Question 7: Neostigmine is used to reverse neuromuscular blockade after surgery. Which agent must always be co-administered with neostigmine to prevent bradycardia?
- Epinephrine
- Atropine (Correct answer)
- Physostigmine
- Pyridostigmine
Correct answer: Atropine
Neostigmine inhibits acetylcholinesterase, increasing ACh at all cholinergic synapses; atropine is co-administered to block the unwanted muscarinic (bradycardic) effects.
NBME Pharmacology 3
A patient receives succinylcholine for rapid sequence intubation.
Which condition represents an absolute contraindication to its use?