Optimizing benzodiazepine treatment of anxiety disorders

Though once the main treatment for anxiety disorders—often as monotherapy¹—benzodiazepines are now primarily used as adjunctive agents.^2-4 Their ability to produce rapid anxiolysis represents a significant therapeutic advantage, but in recent decades their tolerability, class-specific risks, and lack of antidepressant properties contributed to benzodiazepines being largely replaced by selective serotonin reuptake inhibitors (SSRIs) for the pharmacologic treatment of anxiety. This shift within the pharmacologic armamentarium has decreased many clinicians’ familiarity with benzodiazepines.

While benzodiazepines continue to have an important role in managing anxiety disorders, particularly treatment-resistant anxiety,⁴ clinicians must consider the limitations of these agents. Benzodiazepines can be associated with abuse and dependence, and overdose risk when combined with opiates.^5,6 They may cause memory impairment^7,8 and conflicting data suggest they may contribute to the risk of developing cognitive disorders.^9-11 Benzodiazepines also have been associated with falls and fractures,¹² and worse outcomes in patients with posttraumatic stress disorder.¹³ Some studies of patients with chronic obstructive pulmonary disease (COPD) found benzodiazepines may increase the risk of COPD exacerbations and accidental overdose,¹⁴ though others found that was not always the case.¹⁵ Benzodiazepines may be associated with an increased risk of spontaneous abortion when used early in pregnancy.¹⁶ Prospective research in women who were breastfeeding found benzodiazepines may cause sedation in up to 2% of infants.¹⁷

Despite the potential for adverse effects, benzodiazepine use remains common.¹⁸ These medications have a rapid onset of action, are useful for breakthrough symptoms, may enhance treatment adherence, and alleviate activating symptoms of SSRIs. Like other commonly used medications, benzodiazepines have the potential for both harm and benefit.¹⁹ Similar to other medications with tolerability concerns but established efficacy, particularly in treatment-resistant anxiety disorders, it is important to balance “overprescribing … to patients at risk and underusing these effective medications when indicated.”¹⁹ Though the use of benzodiazepines has been discouraged and perceptions have shifted, knowledge of benzodiazepines and benzodiazepine pharmacology also has been degraded contemporaneously.

This article provides a synthesis of the clinically relevant pharmacology of benzodiazepines, with a focus on orally administered benzodiazepines, which are more common in outpatient clinical practice. Specifically, this review describes the pharmacology of benzodiazepines, benzo­diazepine medication interactions, the relationship between pharmacologic characteristics and treatment response/tolerability, and selection and dosing of oral benzodiazepines (Table²⁰).

Benzodiazepine pharmacodynamics

Benzodiazepines act at the gamma-aminobutyric acid (GABA)-A receptor complex and bind allosterically.^21-23 Comprised of 5 glycoprotein subunits (2 alpha subunits, 2 beta subunits, and 1 gamma subunit), the receptor has 2 distinct sites at which the endogenous inhibitory transmitter GABA binds and 1 benzodiazepine binding site. Benzodiazepines bind within a socket created by the alpha and gamma subunits²² and after binding induce a conformational change in the receptor, which enhances GABA binding. There are 2 types of benzodiazepine receptors: BZ1 and BZ2. The subunits play a critical role in driving the pharmacologic characteristics of the receptor.²⁴ BZ1 and BZ2 receptors bind benzodiazepines, although they are differentially distributed within the brain. Binding at BZ1 receptors—which are distributed in cortical, thalamic, and cerebellar regions—contributes to sedation and deleterious effects of benzodiazepines on memory (eg, anterograde amnesia). BZ2 receptors (which contain gamma-2 subunits) are responsible for anxiolytic and muscle-relaxing effects. They are distributed throughout limbic regions and motor tracts, including motor neurons and neurons in the dorsal horn of the spinal cord.²⁴

Benzodiazepines—positive GABA-A receptor allosteric modulators—produce phasic inhibition, largely through the alpha and gamma subunits discussed above. In contrast, newer positive allosteric modulators (eg, zuranolone) bind at the alpha/beta subunits.²⁵ Mechanistically, endogenous neuroactive steroids and nonbenzodiazepine GABA-A–positive allosteric modulators such as zuranolone and ganaxolone also differ in their regulation of GABA-A (downregulated with benzodiazepines and hypothetically upregulated with zuranolone)²⁶ and their synaptic effects (benzodiazepines synaptically vs endogenous neurosteroids and nonbenzodiazpine positive allosteric modulators extrasynaptically).²⁷

From a developmental perspective, benzodiazepines may have less efficacy for anxiolysis and worse tolerability in some pediatric patients,²⁸ although they generally appear effective for immediate use to treat anxiety in acute settings.²⁹ The differences in efficacy and tolerability may be related to pharmacodynamic differences between pediatric populations and adults. GABA receptor expression and function do not reach adult levels until age 14 to 17½ for subcortical regions and age 18 to 22 for cortical regions, although girls reach adult expression of GABA receptors slightly earlier than boys.³⁰ Data from multiple randomized controlled trials of pediatric patients with anxiety disorders do not suggest efficacy as benzodiazepines are poorly tolerated, especially compared to other psychopharmacologic interventions for pediatric anxiety disorders.³⁰

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