Learning Objective
By the end of this section, students should be able to classify β-blockers by selectivity, link their clinical uses to pharmacologic actions, and recognize characteristic adverse effects, with an emphasis on high-yield USMLE Step 1 concepts.
β-Blockers (Beta-Adrenergic Antagonists)
Common Drugs:
Atenolol, Betaxolol, Bisoprolol, Carvedilol, Esmolol, Labetalol, Metoprolol, Nadolol, Nebivolol, Propranolol, Timolol
Clinical Applications and Mechanism
| Application | Action / Mechanism | Examples / Notes |
|---|---|---|
| Angina pectoris | ↓ Heart rate & contractility → ↓ O₂ consumption | All β-blockers |
| Glaucoma | ↓ Aqueous humor production | Timolol |
| Heart failure | Blockade of neurohormonal stress → ↓ cardiac remodeling → ↓ mortality | Bisoprolol, Carvedilol, Metoprolol |
| Hypertension | ↓ Cardiac output, ↓ renin secretion (via β₁ blockade on JG cells) | Most β-blockers |
| Hyperthyroidism / Thyroid storm | Symptom control: ↓ HR, ↓ tremor | Propranolol |
| Hypertrophic cardiomyopathy | ↓ HR → ↑ diastolic filling time → relieves outflow obstruction | β₁-selective agents |
| Migraine prophylaxis | ↓ Nitric oxide–mediated vasodilation | Nonselective β-blockers |
| Myocardial infarction | ↓ O₂ demand (short-term), ↓ mortality (long-term) | Most β-blockers |
| Supraventricular tachycardia / Atrial fibrillation | ↓ AV conduction velocity (Class II antiarrhythmic) | Metoprolol, Esmolol |
| Variceal bleeding (portal hypertension) | ↓ Hepatic venous pressure gradient | Nadolol, Propranolol, Carvedilol |
Adverse Effects
- Cardiovascular: Bradycardia, AV block, worsening heart failure
- CNS: Sedation, sleep disturbances, rarely seizures
- Metabolic: Dyslipidemia (esp. Metoprolol), masked hypoglycemia
- Other: Erectile dysfunction, asthma/COPD exacerbation
- Special note: Acute cocaine-associated chest pain—β-blocker use remains controversial due to potential unopposed α-adrenergic stimulation.
Activity
Selectivity & Key Notes
| Type | Examples | Notes |
|---|---|---|
| β₁-selective antagonists (cardioselective) | Atenolol, Betaxolol, Bisoprolol, Esmolol, Metoprolol | “A–M” alphabet trick |
| Nonselective β-blockers (β₁ = β₂) | Nadolol, Propranolol, Timolol | “N–Z” alphabet trick |
| Nonselective α + β antagonists | Carvedilol, Labetalol | Modified suffixes, not “-olol” |
| Special β₁-selective + β₃ effects | Nebivolol | ↑ NO synthase → ↓ SVR; vasodilatory properties |
USMLE Step 1 Pearls
- β₁-selective → safer in asthma/COPD
- Carvedilol / Labetalol → α + β blockade → use in HF and pregnancy (labetalol)
- Nebivolol → NO-mediated vasodilation
- Propranolol → symptomatic relief in hyperthyroidism
- “First half of alphabet → β₁-selective; second half → nonselective” (mnemonic for quick recall)
