CNS Pharmacology USMLE Step 1 Practice Question
A 32-year-old woman with generalized anxiety disorder presents to the emergency department after becoming unresponsive at a social event. She has taken alprazolam 2 mg daily for 8 months and consumed approximately 240 mL of alcohol (three standard drinks) over 90 minutes. Witnesses report progressive drowsiness, ataxia, and anterograde amnesia. On examination: BP 102/68 mmHg, HR 58 bpm, RR 10 breaths/min, oriented to person only, slurred speech, horizontal nystagmus, and generalized hypotonia. Serum ethanol level is 95 mg/dL. Laboratory studies show normal liver function tests and normal benzodiazepine levels for her stated dose. Which of the following mechanisms best explains her severe CNS depression and altered mental status?
Answer choices
- ACompetitive inhibition at cytochrome P450 3A4 preventing benzodiazepine metabolism
- BInhibition of GABA-A receptor chloride channel opening by both substances acting synergistically
- CAdditive allosteric enhancement of GABA-A receptor sensitivity at multiple binding sitesCorrect answer
- DAlcohol-induced hepatic enzyme induction increasing benzodiazepine clearance
- EAcetaldehyde accumulation impairing NMDA receptor function and benzodiazepine clearance
- FBenzodiazepine-mediated blockade of glutamate receptors potentiated by alcohol-induced GABA disinhibition
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