At the GABA-A chloride channel, benzodiazepines differ from barbiturates because benzodiazepines:

• A Block the chloride channel directly, whereas barbiturates open it
• B Increase the duration of chloride channel opening, whereas barbiturates increase the frequency
• C Increase the frequency of chloride channel opening, whereas barbiturates increase the duration of opening ✓
• D Act only at extrasynaptic GABA-A receptors containing the delta subunit

Explanation

Both drugs are positive allosteric modulators of the GABA-C receptor but at distinct sites. Benzodiazepines bind the interface between alpha and gamma subunits and increase the frequency of channel-opening events in response to GABA. Barbiturates bind elsewhere and prolong each burst of openings, and at high concentrations they can open the channel directly even without GABA, which explains their lower safety margin.

Reference: Katzung Basic and Clinical Pharmacology, 15th ed.

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Written and medically reviewed by the StethoPrep medical team.