Chapter 12  ·  Module 5
Sleep Neurobiology and Comparative Pharmacology
Integrative framework for sedative-hypnotic drug class pharmacology
The Two-Process Model of Sleep Regulation
Process S
Homeostatic Sleep Pressure
  • Driven by adenosine accumulation in the basal forebrain during wakefulness
  • Rises monotonically with wake duration; decays during sleep
  • Determines depth of N3 sleep at next sleep onset
  • Caffeine blocks adenosine receptors, opposing this drive
Process C
Circadian Alerting Signal
  • Generated by the suprachiasmatic nucleus of the hypothalamus
  • Rises through the day, peaks in early evening (opposing sleep pressure to maintain wakefulness)
  • Falls sharply in the evening: opens the circadian gate for sleep onset
  • Communicated via melatonin secretion from the pineal gland
  • Ramelteon reinforces this signal at MT1/MT2 receptors
Sleep Architecture Effects by Drug Class
Drug ClassN3 Slow-Wave SleepREM SleepClinical Consequence
BenzodiazepinesSuppressedSuppressedUnrefreshing sleep despite adequate total sleep time. Rebound REM and N3 on discontinuation (vivid dreams, reinforces use).
Z-DrugsMildly suppressed (less than benzodiazepines at standard doses)Largely preservedBetter architecture than benzodiazepines; advantage diminishes at high doses and in elderly.
Melatonin receptor agonists (ramelteon)PreservedPreservedNormal stage distribution maintained. Trade-off: weakest hypnotic efficacy of any class.
Dual orexin receptor antagonistsPreservedPreserved or increasedMost closely resembles natural sleep. Preferred when sleep quality is the primary goal.
BarbituratesSuppressed at sedating dosesProfoundly suppressedBurst-suppression at anesthetic doses. No role in insomnia treatment.
Propofol (ICU)Partially present (EEG resemblance to N2/N3)SuppressedAccumulates REM debt in ICU patients; may contribute to post-ICU post-traumatic stress disorder.
Insomnia: Drug Selection by Clinical Situation
Sleep-Onset Insomnia
General Adult
  • Zolpidem IR or zaleplon: rapid onset, short duration
  • Zaleplon if middle-of-night awakening with 4+ hours remaining
  • Ramelteon if elderly or substance use disorder history
Sleep-Maintenance Insomnia
Waking During the Night
  • Suvorexant or lemborexant: best evidence for wake-after-sleep-onset reduction
  • Eszopiclone: only Z-drug approved for maintenance
  • Low-dose doxepin (3–6 mg): FDA-approved for maintenance; not scheduled
Special Populations
When Standard Choices Are Problematic
  • Elderly: ramelteon preferred; avoid benzodiazepines and Z-drugs (Beers Criteria)
  • Substance use disorder: ramelteon only
  • Post-traumatic stress disorder: dual orexin receptor antagonist (preserves REM)
  • Obstructive sleep apnea: caution with all; verify CPAP compliance
Anxiety Disorders: Benzodiazepine Role

First-line for chronic anxiety: selective serotonin reuptake inhibitors or serotonin-norepinephrine reuptake inhibitors (durable effect, no tolerance, no dependence). Benzodiazepines: appropriate as bridge therapy during the 2 to 4 week antidepressant onset latency; for acute situational anxiety; and as adjunctive treatment in panic disorder (clonazepam preferred over alprazolam for its longer half-life). Not appropriate as primary long-term anxiolytics. Buspirone: appropriate long-term alternative for generalized anxiety disorder — onset delayed 1 to 4 weeks, no cross-tolerance with benzodiazepines.