Chapter 19: Sedative-Hypnotic and Anxiolytic Drugs

Sedative-Hypnotic and Anxiolytic Drugs explores the physiological transition from adaptive anxiety to chronic states, highlighting the neurological involvement of the amygdala and autonomic pathways in interpreting danger and mediating fear responses. Central to the discussion is the modulation of gamma-aminobutyric acid (GABA), the primary inhibitory neurotransmitter in the brain, via the GABAA receptor-chloride channel complex. The text distinguishes between benzodiazepines, which increase the frequency of channel opening and exhibit a safety-enhancing ceiling effect, and barbiturates, which increase channel opening duration and carry a higher risk of fatal overdose due to their linear dose-response relationship and lack of a ceiling. Special attention is given to sleep architecture, detailing the different stages of non-rapid eye movement (NREM) and rapid eye movement (REM) sleep and how various medications impact these cycles. Newer "Z-drugs" like zolpidem are highlighted for their subunit selectivity, which helps maintain natural sleep patterns while minimizing next-day hangover effects and dependency. The curriculum also introduces orexin receptor antagonists and melatonin agonists as modern alternatives for insomnia management that lack the abuse potential of traditional controlled substances. Crucial pharmacokinetic insights are provided regarding drug metabolism in the liver, specifically the benefits of Phase II conjugation for geriatric patients taking medications like lorazepam, oxazepam, or temazepam to avoid the accumulation of long-acting metabolites. Additionally, the chapter covers nonsedating options such as buspirone for long-term generalized anxiety and the use of beta-blockers like propranolol for situational performance-related stress. It rounds out the study of these central nervous system depressants by discussing the risks of physical dependence, the presentation of withdrawal syndromes, and the application of flumazenil as a specific pharmacological antagonist for reversing benzodiazepine-induced depression.