Zolpidem

Zolpidem, the active moiety of zolpidem tartrate, is a hypnotic substance with a chemical structure that is not related to the structure benzodiazepines, barbiturates, pyrrolopyrazines, pyrazolopyrimidines or other drugs exerting hypnotic effects. It interacts with a GABA-BZ receptor complex and shares various pharmacological properties with the benzodiazepine class of drugs.

Subunit binding of the GABAA receptor chloride channel macromolecular complex is thought to lead to the sedative, anticonvulsant, anxiolytic, and myorelaxant drug effects of zolpidem. The main regulatory site of the GABAA receptor complex can be found on its alpha (α) subunit and is called the benzodiazepine (BZ) or omega (ω) receptor. At least three different subtypes of the (ω) receptor have been identified to this date.

In contrast to benzodiazepine drugs, which are found to modulate all benzodiazepine receptor subtypes in a non-selective fashion, zolpidem binds the (BZ1) receptor specifically with a potent affinity for the alpha 1/alpha 5 subunits (in vitro). More recent studies suggest that zolpidem binds primarily to the alpha 1, 2, and 3 subunits of the GABA receptor, and not the alpha 5 subunit.

The (BZ1) receptor is found primarily on the Lamina IV of the brain sensorimotor cortical regions, substantia nigra (pars reticulata), cerebellum molecular layer, olfactory bulb, ventral thalamic complex, pons, inferior colliculus, and globus pallidus. Specific and selective binding of zolpidem on the (BZ1) receptor is not considered absolute, however, this binding could potentially explain the relative lack of myorelaxant and anticonvulsant activity in animal studies in addition to the preservation of deep sleep (stages 3 and 4) in human studies of zolpidem at hypnotic doses.