Beta-Blockers
The NP-board angle on beta-blockers is mortality benefit and cardioselectivity. Beta-blockers reduce heart rate, contractility, and renin release, lowering blood pressure and myocardial oxygen demand. They reduce mortality post-MI and in HFrEF — the three with HFrEF evidence are metoprolol succinate, carvedilol, and bisoprolol. Cardioselective agents (metoprolol, atenolol, bisoprolol) preferentially block beta-1 and are safer in COPD and asthma; non-selective agents (propranolol, nadolol) also block beta-2 and risk bronchospasm. Carvedilol has alpha-1 activity and is preferred in HFrEF with hypertension. Board questions cluster around HFrEF agent selection, holding for symptomatic bradycardia or hypotension, and recognizing the masked-hypoglycemia warning in diabetics on insulin.
📖 Overview
Beta-blockers block β-adrenergic receptors, decreasing heart rate, cardiac contractility, and myocardial oxygen demand. Cardioselective agents (metoprolol, atenolol) preferentially block β₁ (heart). Non-selective agents (propranolol) also block β₂ (lungs → bronchoconstriction). Mixed α/β-blockers (carvedilol, labetalol) add peripheral vasodilation.
⚙️ Mechanism of Action
β₁ blockade: ↓HR, ↓contractility, ↓renin. β₂ blockade: bronchoconstriction, vasoconstriction, ↓hepatic glycogenolysis. α₁ blockade (carvedilol/labetalol): vasodilation.
💎 Board Pearls
- 🚨 CHF MORTALITY BENEFIT: metoprolol succinate, carvedilol, bisoprolol. Never start acutely decompensated — start low, go slow when stable.
- ⚠️ Mask signs of hypoglycemia (except sweating) — caution in insulin-using diabetics.
- 🫁 Asthma/COPD: avoid non-selective; cardioselective OK at low dose.
- 🤰 Labetalol = pregnancy HTN gold standard (along with methyldopa, nifedipine).
- 💡 Non-cardiac uses: propranolol (tremor, migraine prophylaxis, performance anxiety, thyroid storm).
- 🚫 Abrupt discontinuation → rebound HTN/tachycardia → taper over 1–2 weeks.
💊 Drugs in This Class
- Metoprolol — Lopressor (tartrate), Toprol-XL (succinate)HTN, angina, post-MI, CHF (succinate only), rate control in a-fib.
- Carvedilol — CoregCHF (HFrEF), HTN, post-MI with LV dysfunction.
- Propranolol — InderalHTN, angina, migraine prophylaxis, essential tremor, thyrotoxicosis/thyroid storm, performance anxiety.
- Labetalol — Trandate, NormodynePregnancy-induced HTN, hypertensive emergency, resistant HTN.
Practice Questions
Which of the following beta-blockers is considered CARDIOSELECTIVE (β1-preferring at standard doses)?
Sources
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