zolpidem

MECHANISM: Positive allosteric modulator of the GABA-A receptor at the benzodiazepine binding site, selective for alpha-1 subunit-containing receptors (BZ1/omega-1). This increases the FREQUENCY of Cl- channel opening (like benzodiazepines; barbiturates increase DURATION), causing neuronal hyperpolarization and sedation. Alpha-1 selectivity explains strong hypnotic effects with weak anxiolytic (alpha-2), muscle relaxant (alpha-2/3/5), and anticonvulsant activity. Effects are reversed by flumazenil (competitive BZ-site antagonist).

PHARMACOKINETICS: Rapid onset (~30 min) and short half-life (~2-3 h), so it helps with sleep onset more than sleep maintenance. Metabolized by hepatic CYP3A4 (major) plus CYP2C9 and CYP1A2 to inactive metabolites. Dose reduction is needed in elderly patients, hepatic impairment, and women (FDA recommends lower starting doses: 5 mg IR and 6.25 mg ER for women, because of slower clearance and higher next-morning blood levels). CYP3A4 inhibitors (ketoconazole, ritonavir, clarithromycin) raise levels; inducers (rifampin, carbamazepine, phenytoin, St. John's wort) lower efficacy.

CLINICAL USE: Short-term treatment of insomnia (sleep-onset). First-line insomnia treatment is CBT-I (cognitive behavioral therapy for insomnia) plus sleep hygiene; pharmacotherapy is adjunctive.

ADVERSE EFFECTS (high-yield): - Complex sleep behaviors (sleepwalking, sleep-driving, sleep-eating, sleep-sex) with anterograde amnesia for the event. The FDA boxed warning (2019) covers eszopiclone, zaleplon, and zolpidem. - Anterograde amnesia, next-day psychomotor impairment (driving risk), dizziness, headache, drowsiness. - Hallucinations, confusion, and falls/fractures in elderly patients (Beers criteria: avoid). - CNS/respiratory depression when combined with alcohol, opioids, or other sedatives. - Tolerance, dependence, and rebound insomnia are less common than with benzodiazepines but still occur. It is a Schedule IV controlled substance. - Overdose: CNS depression; treat supportively, and flumazenil can be used.

DISTINGUISHING POINTS: - Z-drugs: zolpidem, zaleplon (shortest half-life, ~1 h), eszopiclone (longest, ~6 h; metallic taste). All act at the BZ1/alpha-1 site. - Benzodiazepines: nonselective at BZ1 and BZ2, so they also have anxiolytic, anticonvulsant, and muscle relaxant effects; they alter sleep architecture (suppress REM and slow-wave sleep). Zolpidem has less effect on sleep architecture. - Other insomnia agents: ramelteon (melatonin MT1/MT2 agonist; no abuse potential), suvorexant/lemborexant/daridorexant (orexin receptor antagonists; may cause sleep paralysis and narcolepsy-like symptoms), doxepin low-dose (H1 antagonist), trazodone (off-label). - Paradoxical case: zolpidem has been reported to transiently improve consciousness in some patients with disorders of consciousness (e.g., after brain injury), and to improve dystonia or Parkinson's symptoms in case reports.

BOARD PEARL: A patient found at night eating, cooking, or driving with no memory of it the next morning, after starting a new sleep aid, points to zolpidem. Know that flumazenil reverses it and that benzodiazepine-site agents increase frequency of Cl- channel opening.