Zolpidem is preferred over diazepam for insomnia because it selectively acts on which GABA-A receptor subunit combination?

• A Alpha-2/alpha-3 subunits (anxiolytic/myorelaxant subtype)
• B Alpha-1 subunit (sedative/hypnotic subtype), with relative sparing of alpha-2 and alpha-3 ✓
• C Delta subunit-containing extrasynaptic receptors mediating tonic inhibition
• D Beta-3 subunit, which mediates anaesthetic effects

Explanation

Zolpidem is a non-benzodiazepine (imidazopyridine) that binds the benzodiazepine site on GABA-A receptors but selects for receptors containing the alpha-1 subunit, which are responsible for sedative and hypnotic effects. Receptors containing alpha-2 and alpha-3 subunits mediate anxiolytic, myorelaxant, and anticonvulsant effects; zolpidem's relative sparing of these reduces daytime sedation, muscle relaxation, and tolerance compared to classical benzodiazepines.

Reference: KD Tripathi, Essentials of Medical Pharmacology, 8th ed.

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