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PH3.6 | PH3.6 | Anxiolytics and Goals of Anxiety Pharmacotherapy — SDL Guide — SDL Guide (Part 2)
Benzodiazepines as Anxiolytics — PK, PD, Uses, and ADRs
For the mechanism of benzodiazepines (GABA-A frequency potentiation, subunit pharmacology) and their general pharmacokinetics, refer to the Sedative-Hypnotic Agents module (PH3.2). Here the focus is on their role and limitations specifically in anxiety disorders.
Benzodiazepines that are commonly used in anxiety include: diazepam (long-acting — suitable for short-term GAD; muscle relaxant property useful for somatic tension), lorazepam (intermediate-acting; hepatic impairment; acute panic), alprazolam (short-acting, high potency — widely used for panic disorder, but high dependence potential, particularly with abrupt discontinuation), and clonazepam (long-acting; panic disorder, social anxiety; also anticonvulsant).
Why BZDs are NOT appropriate for long-term anxiety management:
- Tolerance: the anxiolytic effect diminishes over weeks as GABA-A receptors down-regulate (reduce in number) in response to chronic potentiation — patients need increasing doses to get the same effect.
- Dependence: physical dependence develops within 4-6 weeks of daily use; withdrawal produces rebound anxiety that is often more severe than the original disorder — creating a vicious cycle.
- Cognitive impairment: chronic BZD use is associated with memory impairment, psychomotor slowing, and increased accident/fall risk (especially in elderly).
- Lack of antidepressant activity: many anxiety disorders are comorbid with depression; SSRIs treat both — BZDs treat neither.
- Withdrawal seizures: abrupt discontinuation after prolonged use (as in alcohol withdrawal) — must taper.
ADRs of BZD anxiolytics: sedation, cognitive blunting, anterograde amnesia, ataxia, paradoxical agitation (in elderly, children), respiratory depression with alcohol or other CNS depressants. Alprazolam has the highest dependence liability among BZDs.
Non-BZD Anxiolytics — Buspirone, SSRIs, and Others
Buspirone is the principal non-BZD non-SSRI anxiolytic. Its mechanism — partial agonism at 5-HT₁A receptors — is fundamentally different from BZDs: it does not act on GABA-A at all. Presynaptically, it activates 5-HT₁A autoreceptors on dorsal raphe neurons, reducing serotonin firing (acute phase, may initially slightly worsen anxiety in some patients). Over 2-4 weeks, desensitisation of these autoreceptors and postsynaptic neuroplastic changes produce the anxiolytic effect. Clinical profile:
- Delayed onset (2-4 weeks) — patients previously accustomed to immediate BZD relief may feel 'it is not working'; counselling on the delay is essential
- No sedation (suitable for patients who need to drive or operate machinery)
- No dependence or abuse potential (not a controlled substance)
- No cross-tolerance with BZDs — patients switching from chronic BZDs to buspirone will NOT have their BZD withdrawal symptoms relieved by buspirone
- Effective specifically for GAD — not for panic disorder (where rapid relief is needed), not for acute anxiety episodes
SSRIs/SNRIs as anxiolytics: these are the first-line pharmacological treatment for all chronic anxiety disorders per international guidelines. Mechanism is via SERT blockade — increased synaptic 5-HT over weeks drives neuroplastic changes in fear-circuit regulation. Evidence-based indications: GAD, panic disorder, social anxiety disorder, PTSD (first-line), OCD (high doses required, long-term). The same SSRI-related cautions apply (serotonin syndrome risk with MAOIs/tramadol; discontinuation syndrome on abrupt cessation).
Beta-blockers (propranolol): peripheral β₁/β₂ antagonism blocks the sympathomimetic manifestations of anxiety (tremor, tachycardia, palpitations, sweating). Used PRN for situational performance anxiety (e.g., before a public speaking event). Dose: propranolol 10-40 mg orally 30-60 min before the event. No effect on the central worry or fear experience. NOT appropriate for chronic anxiety disorders.
Hydroxyzine: first-generation H₁ antihistamine with mild anxiolytic effect via central histaminergic blockade. Used for pre-operative anxiety and mild situational anxiety. No dependence potential.
SELF-CHECK
A patient with GAD has been on diazepam for 3 months. You decide to switch her to buspirone. She returns at 2 weeks saying buspirone 'is not working' and she 'feels worse'. What is the correct pharmacological explanation and clinical response?
A. Buspirone is ineffective for GAD — discontinue and restart diazepam
B. Buspirone has a delayed onset of 2-4 weeks and has no cross-tolerance with BZDs — her withdrawal anxiety from diazepam tapering is not relieved by buspirone; continue buspirone (anxiolytic effect will develop) and manage BZD withdrawal by gradual tapering
C. Buspirone is causing serotonin syndrome — stop immediately
D. Buspirone dose is too low — double the dose and reassess next week
Reveal Answer
Answer: B. Buspirone has a delayed onset of 2-4 weeks and has no cross-tolerance with BZDs — her withdrawal anxiety from diazepam tapering is not relieved by buspirone; continue buspirone (anxiolytic effect will develop) and manage BZD withdrawal by gradual tapering
Two pharmacological issues explain her experience: (1) buspirone's anxiolytic effect has a delayed onset of 2-4 weeks — it is not expected to provide immediate relief; and (2) buspirone has NO cross-tolerance with BZDs — it cannot suppress BZD withdrawal symptoms (which may be worsening her anxiety at 2 weeks into the switch). The correct approach is to continue buspirone (its effect will emerge by 4 weeks), while simultaneously tapering diazepam gradually (not abruptly) to prevent withdrawal seizures and manage rebound anxiety.
SELF-CHECK
What is the pharmacological first-line treatment for generalised anxiety disorder (GAD) requiring long-term pharmacotherapy?
A. Long-term diazepam — most effective and most rapidly acting anxiolytic available
B. Alprazolam — high potency BZD proven most effective in GAD trials
C. SSRI or SNRI (e.g., escitalopram, venlafaxine) — first-line for chronic anxiety disorders; no dependence liability
D. Hydroxyzine — safest anxiolytic with no drug interactions
Reveal Answer
Answer: C. SSRI or SNRI (e.g., escitalopram, venlafaxine) — first-line for chronic anxiety disorders; no dependence liability
SSRIs and SNRIs are the first-line pharmacological treatment for GAD and all other chronic anxiety disorders per international guidelines (including NICE, WHO). They address the underlying serotonergic dysregulation in the fear circuit, have no dependence liability, have antidepressant activity (important given high comorbidity with depression), and are effective on continuous use. Benzodiazepines are highly effective short-term (≤4 weeks) but cause tolerance, dependence, and cognitive impairment on long-term use — making them appropriate only as short-term adjuncts, not as monotherapy for chronic GAD.
SELF-CHECK
A student physician is anxious before her first clinical presentation. She has no psychiatric diagnosis but experiences palpitations and hand tremor that she fears will be noticed. Which pharmacological option is most appropriate PRN for this situational performance anxiety?
A. Diazepam 5 mg oral — rapid anxiolysis will eliminate all performance anxiety
B. Buspirone 10 mg oral — fast-acting serotonergic anxiolytic ideal for acute performance anxiety
C. Propranolol 20 mg oral — blocks peripheral sympathetic manifestations (tremor, palpitations) without sedation or cognitive impairment
D. Sertraline 50 mg oral — SSRI will reduce anxiety within 2 hours
Reveal Answer
Answer: C. Propranolol 20 mg oral — blocks peripheral sympathetic manifestations (tremor, palpitations) without sedation or cognitive impairment
Propranolol (a non-selective beta-blocker) blocks β₁ and β₂ adrenoceptors peripherally, preventing the sympathomimetically-mediated somatic symptoms of performance anxiety — tremor (β₂-mediated), palpitations and tachycardia (β₁-mediated), and sweating. It has no sedating or cognitive-impairing effect, making it suitable for a situation requiring peak mental performance. Given PRN 30-60 min before the event. Diazepam would cause sedation and impair performance. Buspirone has a 2-4 week delayed onset — useless for acute use. SSRIs have no acute anxiolytic effect.
CLINICAL PEARL
Prescribing BZDs for chronic anxiety is solving the wrong problem. The 'anxiety' a patient feels between BZD doses after 3 months of daily use is largely BZD withdrawal anxiety — not the original disorder. Each dose provides relief, but also deepens dependence. The patient experiences the drug as 'essential' because without it they feel worse than before they started (rebound beyond baseline). Breaking this cycle requires gradual tapering (switch to long-acting diazepam, reduce by 10-25% every 2 weeks) combined with starting an SSRI and CBT.