Beta-Blockers
On this page
Direct answer
Beta-blockers are competitive antagonists at beta-adrenergic receptors that reduce heart rate, contractility, conduction and renin release, lowering cardiac oxygen demand and blood pressure. They are cornerstone therapy in hypertension, angina, arrhythmias, heart failure with reduced ejection fraction and after myocardial infarction. Their defining hazard is bronchospasm from beta-2 blockade, which makes asthma a contraindication, and they must never be stopped abruptly.
What you must remember
- Classification: non-selective (propranolol, nadolol, timolol); cardioselective beta-1 blockers (atenolol, metoprolol, bisoprolol, and the ultra-short-acting intravenous esmolol); agents with intrinsic sympathomimetic activity (pindolol, acebutolol); combined alpha and beta blockers (labetalol, carvedilol); and distinctive agents — nebivolol (nitric-oxide-mediated vasodilatation) and sotalol (also a class III antiarrhythmic).
- Cardiovascular uses: hypertension, effort angina, supraventricular arrhythmias and rate control in atrial fibrillation, post-infarction protection, and heart failure with reduced ejection fraction — for which bisoprolol, metoprolol succinate and carvedilol have mortality benefit; start low, go slow, and never initiate during acute decompensation.
- Non-cardiovascular uses: thyrotoxicosis, essential tremor, migraine prophylaxis, variceal bleeding prophylaxis in portal hypertension (propranolol), anxiety symptoms, and glaucoma (timolol eye drops reduce aqueous humour formation).
- Adverse effects: bradycardia and heart block, fatigue and cold extremities, worsening peripheral vascular disease and Raynaud phenomenon, bronchospasm, nightmares and insomnia with lipophilic agents, and erectile dysfunction.
- In insulin-treated diabetics they mask adrenergic warning signs of hypoglycaemia (tremor, palpitations) and blunt beta-2-mediated recovery — a favourite exam point.
- Contraindications: asthma (non-selective agents absolutely), second- and third-degree heart block, severe bradycardia, decompensated heart failure, and cocaine-induced ischaemia, where unopposed alpha activity worsens vasoconstriction.
- Never withdraw abruptly — receptor upregulation causes rebound tachycardia, angina and even infarction; taper over one to two weeks.
Common confusion
Students confuse the safety of cardioselective and non-selective agents in airway disease. Beta-1 selectivity is relative and dose-dependent, so atenolol or metoprolol are merely safer, not safe, in asthma; propranolol remains absolutely contraindicated. A second puzzle is why negative inotropes help heart failure — chronic sympathetic overdrive ultimately harms the failing heart, and blockade reverses remodelling, which is why benefits emerge over weeks.
Exam-focused takeaway
Theory answers should classify the drugs with one representative each, list uses by system, then adverse effects, contraindications and the withdrawal warning. Viva examiners ask how beta-blockers mask hypoglycaemia and which agent suits glaucoma or thyrotoxicosis. MCQs repeatedly test timolol in glaucoma, esmolol's short action, propranolol's first-pass metabolism and portal hypertension role, and avoidance in cocaine-related chest pain.
Frequently asked questions
Which beta-blockers are preferred in heart failure?
Bisoprolol, metoprolol succinate and carvedilol, which carry evidence of mortality benefit; they are introduced at low dose once the patient is stable.
Why are beta-blockers dangerous in asthma?
Beta-2 blockade on bronchial smooth muscle causes constriction; non-selective agents are contraindicated and even cardioselective ones need caution.
Why must beta-blockers never be stopped suddenly?
Chronic blockade upregulates receptors, so abrupt withdrawal causes rebound sympathetic overactivity with tachycardia, angina and arrhythmia risk.
How do they mask hypoglycaemia in diabetics?
They abolish adrenergic warning signs such as tremor and palpitations, and beta-2 blockade slows hepatic glycogenolysis, delaying glucose recovery.
Which beta-blocker is used in glaucoma?
Timolol, as eye drops that lower intraocular pressure by reducing aqueous humour production.