3 Clinical psychopharmacology3.3 Pharmacodynamics
3.3.6.4 Beta blockers
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Written by Resident Doctor Committee · Published
Receptors and selectivity
Receptor | Site and action |
|---|---|
Beta-1 | Heart rate and contractility; renin release |
Beta-2 | Bronchial smooth muscle relaxation; skeletal muscle tremor |
Propranolol blocks both beta-1 and beta-2 receptors, and its beta-2 blockade can narrow the airways, so it is contraindicated in asthma.
Cardioselective beta-blockers such as atenolol and bisoprolol mainly block beta-1, though this selectivity falls at higher doses.
Propranolol is lipophilic and enters the brain, whereas atenolol is hydrophilic and largely stays out.
Antipsychotic-induced akathisia
Propranolol is the best-evidenced symptomatic treatment, acting through central blockade.
Review the antipsychotic dose and choice first, and check pulse and blood pressure before starting.
Antimuscarinics mainly help coexisting parkinsonism.
Lithium tremor
Tremor | Features | Meaning |
|---|---|---|
Fine postural | Seen on outstretched hands, worse with caffeine or anxiety | Drug effect; propranolol reasonable |
Coarse, with ataxia | Vomiting, confusion, dysarthria | Lithium toxicity needing urgent assessment |
Propranolol treats a fine postural lithium tremor only when the lithium level is therapeutic and toxicity has been excluded.
Adverse effects and stopping
Bradycardia and hypotension cause fatigue, dizziness and cold extremities.
Lipophilic beta-blockers can cause nightmares.
Beta-blockade can mask the tremor and palpitations of hypoglycaemia, while sweating persists.
Stopping abruptly after regular use causes rebound tachycardia and tremor, so people taper sustained use over one to two weeks.