Beta blockers.
Almost everything asked about beta blockers comes from one question: which beta receptors does this particular drug block. Get that right and the therapeutic effects, the side effects and the contraindications all fall out of it without being learned separately.
The mechanism in one sentence
Beta blockers occupy beta-adrenergic receptors so that circulating adrenaline and noradrenaline cannot act on them.
Beta receptors come in subtypes that sit in different tissues. β₁ receptors are concentrated in the heart, where stimulation raises rate and force of contraction, and in the kidney, where they drive renin release. β₂ receptors sit in bronchial smooth muscle, in blood vessels supplying skeletal muscle, in the liver and in skeletal muscle itself. A beta blocker binds these receptors without activating them, so the sympathetic signal arrives and finds the door shut. Whether a given drug blocks only β₁ or both subtypes is what separates one beta blocker from another, and it is the single fact worth knowing about any of them.
Members of the class
| Drug | What sets it apart |
|---|---|
| Propranolol | Non-selective and lipophilic, so it blocks β₂ as well as β₁ and crosses into the brain. |
| Atenolol | β₁ selective and hydrophilic, so fewer central effects and less airway risk. |
| Bisoprolol | Highly β₁ selective; one of the agents with heart failure mortality evidence. |
| Metoprolol | β₁ selective but lipophilic, so more CNS penetration than atenolol. |
| Carvedilol | Blocks β₁, β₂ and α₁, so it causes vasodilation as well as rate control. |
| Sotalol | Beta blockade plus potassium channel blockade, which is why it prolongs the QT interval. |
What the class is used for
- Angina and secondary prevention after myocardial infarction, by reducing cardiac work
- Heart failure with reduced ejection fraction, using specific agents and introduced slowly
- Rate control in atrial fibrillation and other tachyarrhythmias
- Hypertension, though no longer first-line in most guidelines
- Non-cardiac uses including essential tremor, migraine prophylaxis and thyrotoxicosis
Side effects, derived from the mechanism
Each entry below follows from the mechanism above rather than being a separate fact. Read the middle column as the answer to the question, why would that happen.
| Effect | Why it follows |
|---|---|
| Bronchospasm | β₂ blockade in bronchial smooth muscle removes the signal that keeps airways dilated. This is why non-selective agents are avoided in asthma and why selectivity matters clinically rather than academically. |
| Bradycardia and heart block | β₁ blockade at the SA and AV nodes is the intended effect taken further than wanted, which is why it appears at higher doses and alongside other rate-limiting drugs. |
| Cold extremities and fatigue | Reduced cardiac output plus loss of β₂-mediated vasodilation in skeletal muscle beds leaves less blood flow where exercise demands it. |
| Masked hypoglycaemia | The tremor and palpitations that warn of a falling glucose are β-mediated, so blockade removes the warning while leaving the danger. Sweating is cholinergic and usually persists. |
| Vivid dreams and nightmares | Lipophilic agents such as propranolol and metoprolol cross the blood-brain barrier; hydrophilic agents such as atenolol largely do not. |
Contraindications and cautions
- Asthma, particularly with non-selective agents
- Severe bradycardia, second or third degree heart block, and decompensated heart failure
- Caution in peripheral arterial disease and in insulin-treated diabetes with hypoglycaemia unawareness
The part you cannot derive
Abrupt withdrawal after long-term use can precipitate rebound tachycardia, angina or infarction, because chronic blockade upregulates beta receptors and removing the drug exposes them all at once. This one does not follow from acute mechanism and has to be learned: taper rather than stop.
Exam traps
Selectivity is relative, not absolute
A β₁ selective agent still blocks β₂ at high enough doses. Exams test this by giving a cardioselective drug at a high dose to an asthmatic patient.
Sotalol is not a plain beta blocker
Its class III potassium channel activity prolongs QT, so it carries a torsades risk that the other agents on this list do not.
Carvedilol lowers blood pressure by two routes
The α₁ blockade adds vasodilation, which is why first-dose hypotension is more of an issue than with a pure beta blocker.
Members of this class that get confused
Within a class, the members differ on one property at a time, and that property is what exam questions are usually built on. These pairs split cleanly.
- Propranolol vs Atenolol — Propranolol is non-selective and lipophilic; atenolol is beta-1 selective and hydrophilic.
- Metoprolol vs Atenolol — Both are beta-1 selective, so selectivity does not separate them.
- Salbutamol vs Salmeterol — Salbutamol acts within minutes and lasts a few hours, making it the reliever.
Test yourself on this
Reading a mechanism and being able to retrieve it under time are different skills, and only the second one is examined. These are free and need no account.
- Cardiovascular pharmacology practice questions — 10 questions with explanations
- Selective versus non-selective beta blockers
- How beta blockers mask hypoglycaemia
- Propranolol vs atenolol
- Creatinine clearance calculator (Cockcroft-Gault) — free calculator with a worked example
Common questions
Which beta blockers are cardioselective?
Bisoprolol, atenolol and metoprolol are β₁ selective. Propranolol, carvedilol and sotalol are not. Selectivity is relative and falls away at higher doses, so a cardioselective agent is safer in airway disease rather than safe.
Why do beta blockers cause tiredness?
Blocking β₁ reduces cardiac output and blocking β₂ removes vasodilation in exercising muscle, so less blood reaches the tissues that are asking for it. Lipophilic agents add a central component on top.
Can someone with asthma take a beta blocker?
Non-selective agents are contraindicated. A cardioselective agent may be used with caution where the cardiac indication is strong, but that is a prescribing decision made case by case, not a general rule.
Other drug classes
ACE inhibitors · Statins · Anticoagulants · Diuretics · Opioids · Benzodiazepines · All drug classes
Study aid only. This page is written for learning and examination practice. It is not medical advice, not clinical decision support, and must never be used to make a decision about a real patient. Always verify against your local formulary, the product literature and a qualified pharmacist. See our medical disclaimer.
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