U01.05.027 β-blockers

β-blockers are a diverse group of medications used to treat a variety of cardiovascular and non-cardiovascular conditions by blocking β-adrenergic receptors. They are categorized based on their selectivity and specific actions.

Common β-Blockers

Selective (β1 > β2): Acebutolol, Atenolol, Betaxolol, Bisoprolol, Esmolol, Metoprolol
Nonselective (β1 = β2): Nadolol, Pindolol, Propranolol, Timolol
Nonselective α- and β-antagonists: Carvedilol, Labetalol
Unique Mechanism: Nebivolol

Applications, Actions, and Examples

Application	Actions	Examples/Notes
Angina pectoris	↓ Heart rate and contractility → ↓ O₂ consumption	Used to improve oxygen demand-supply balance.
Glaucoma	↓ Aqueous humor production	Timolol commonly used.
Heart failure	↓ Mortality	Bisoprolol, Carvedilol, Metoprolol (Curb Mortality).
Hypertension	↓ Cardiac output, ↓ Renin secretion	Mediated via β1-receptor blockade on JG cells.
Hyperthyroidism/Thyroid storm	Symptom control (↓ Heart rate, ↓ Tremor)	Propranolol is effective.
Hypertrophic cardiomyopathy	↓ Heart rate → ↑ Filling time, ↓ Obstruction	Improves diastolic function.
Myocardial infarction	↓ O₂ demand (acute), ↓ Mortality (chronic)	Long-term survival benefit.
Supraventricular tachycardia	↓ AV conduction velocity (Class II action)	Metoprolol, Esmolol commonly used.
Variceal bleeding	↓ Portal hypertension, ↓ Hepatic venous pressure	Nadolol, Propranolol, Carvedilol for prophylaxis.

Adverse Effects

Cardiovascular: Bradycardia, AV block, heart failure (HF).
CNS: Seizures, sleep disturbances.
Metabolic: Dyslipidemia (notable with Metoprolol).
Respiratory: Worsened asthma/COPD symptoms.
Other: Erectile dysfunction.

Controversy:

Use in acute cocaine-associated chest pain remains debatable due to potential for unopposed α-adrenergic stimulation.

Selectivity Characteristics

Type	Examples	Mnemonic/Notes
β1-selective	Acebutolol, Atenolol, Betaxolol, Bisoprolol, Esmolol, Metoprolol	A-M for β1 (1st half of alphabet).
Nonselective (β1 = β2)	Nadolol, Pindolol, Propranolol, Timolol	N-Z for β2 (2nd half of alphabet).
Nonselective α- and β-	Carvedilol, Labetalol	Ends with modified suffixes (not “-olol”).
Nebivolol	Combines β1-blockade and β3-receptor stimulation	↑ NO → Vasodilation and ↓ Systemic vascular resistance.

Points to Remember

“Selective” β1-blockers are cardioselective and preferred for asthma or COPD.
“Nonselective” β-blockers affect both β1 and β2 receptors, impacting the heart and lungs.
Nebivolol offers vasodilatory properties through nitric oxide (NO) production.
Certain β-blockers (e.g., Bisoprolol, Carvedilol, Metoprolol) reduce mortality in heart failure.
Timolol is crucial for glaucoma management, while propranolol plays a role in thyroid storm and migraine prevention.

Bibliography

First Aid for the USMLE Step 1 (2024 Edition).
Goodman & Gilman’s The Pharmacological Basis of Therapeutics, 13th Edition.
Katzung’s Basic and Clinical Pharmacology, 15th Edition.

USMLE Step 1 Review Series

Curriculum