A 42-year-old man is brought to the emergency department with altered mental status and respiratory depression. His wife reports he ingested an unknown quantity of medication 2 hours ago. EEG shows excess frontocentral fast activity at 15–25 Hz with high amplitude, symmetrical across both hemispheres, persisting into drowsiness. The pattern marked **A** in the diagram is consistent with which class of drug?

Question

Accepted Answer

B. GABA-A receptor potentiators (benzodiazepines and barbiturates). ## Why GABA-A receptor potentiators is right

The excess frontocentral fast beta activity at 15–25 Hz (marked **A**) is a characteristic and highly specific EEG signature of GABA-A receptor potentiating drugs, principally benzodiazepines (diazepam, lorazepam, midazolam, clonazepam, alprazolam) and barbiturates (phenobarbital, thiopental, pentobarbital). Both drug classes enhance GABAergic inhibition through allosteric modulation—benzodiazepines increase the frequency of GABA-A chloride channel opening, while barbiturates increase the duration of opening and can directly open the channel at high doses. The resulting widespread cortical inhibition paradoxically generates this excess beta activity, which is moderate to high amplitude, predominantly frontal and frontocentral, symmetrical, continuous, and persists during drowsiness and early sleep. The amplitude correlates with serum drug level. This EEG pattern is a reliable marker of sedative-hypnotic exposure and is used clinically to confirm drug overdose and to guide EEG-titrated coma induction in refractory status epilepticus (Niedermeyer's Electroencephalography 7e).

## Why each distractor is wrong

- **Dopamine D2 receptor antagonists**: Antipsychotics do not produce excess beta activity. They may cause slowing of background rhythm or other EEG changes, but the characteristic 15–25 Hz frontocentral beta pattern is not associated with dopamine antagonism.
- **Monoamine oxidase inhibitors**: MAOIs do not produce this EEG pattern. They are associated with potential hypertensive crises and serotonergic effects but do not generate the drug-induced beta activity seen with GABA-A potentiators.
- **Selective serotonin reuptake inhibitors**: SSRIs do not produce excess beta activity. While they may affect overall EEG patterns, the specific 15–25 Hz symmetrical frontocentral beta signature is not characteristic of serotonergic drugs.

**High-Yield:** Drug-induced beta activity (15–25 Hz, frontocentral, symmetrical, persistent into sleep) is pathognomonic for GABA-A potentiators; asymmetry of this pattern suggests an underlying structural lesion on the side with reduced beta.

[cite: Niedermeyer's Electroencephalography 7e; Schomer & Lopes da Silva]

Answer

A. Selective serotonin reuptake inhibitors (SSRIs)

Answer

C. Monoamine oxidase inhibitors (MAOIs)

Answer

D. Dopamine D2 receptor antagonists (antipsychotics)

Explanation

Why GABA-A receptor potentiators is right

Why each distractor is wrong

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