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# Beta-Blockers
## Overview
Beta-adrenergic receptor antagonists block the binding of catecholamines (epinephrine/norepinephrine) to beta receptors. They are categorized by selectivity (β1-cardioselective vs. non-selective) and intrinsic sympathomimetic activity (ISA). Some possess additional alpha-blocking properties (e.g., carvedilol, labetalol).
## Primary Indications
Hypertension, stable angina, heart failure with reduced ejection fraction (HFrEF), post-myocardial infarction (MI), atrial fibrillation (rate control), and migraine prophylaxis.
## Adult Dosing
* **Metoprolol Succinate (ER):** Start 25–50 mg daily; titrate to max 400 mg/day (for HF).
* **Atenolol:** 25–50 mg daily; max 100 mg/day.
* **Bisoprolol:** 2.5–5 mg daily; max 20 mg/day.
* **Carvedilol:** 3.125 mg BID; titrate to target 25 mg BID (or 80 mg daily for ER).
* **Propranolol (Immediate):** 20–40 mg BID; daily maintenance varies widely by indication.
*Note: Dosing is highly indication-specific; refer to local protocols for acute cardiac events or titration schedules.*
## Pediatric Dosing
Dosing is weight-based.
* **Atenolol:** 0.5–1 mg/kg/day (Max 2 mg/kg/day).
* **Propranolol:** 0.5–1 mg/kg/day divided 2–4 times daily (Max 8 mg/kg/day).
* **Metoprolol:** 1–2 mg/kg/day divided BID (Max 6 mg/kg/day).
*Strictly verify pediatric dosing via weight/BSA calculation per specific institutional guidelines.*
## Dose Adjustments
* **Renal Impairment:** Atenolol requires dose reduction/dosing interval adjustment. Most lipophilic beta-blockers (metoprolol, propranolol) are hepatically metabolized and generally do not require adjustments.
* **Hepatic Impairment:** Reduce starting doses for carvedilol, labetalol, and propranolol.
## Contraindications
Second- or third-degree heart block (without a pacemaker), cardiogenic shock, bradycardia, severe peripheral arterial disease, and severe/uncontrolled reactive airway disease (asthma).
## Adverse Effects
Bradycardia, hypotension, fatigue, dizziness, sexual dysfunction, cold extremities, and masking of hypoglycemia symptoms (tachycardia) in diabetic patients. Abrupt withdrawal may cause rebound hypertension or tachycardia.
## Key Drug Interactions
* **CYP2D6 Inhibitors:** (e.g., fluoxetine, paroxetine) increase levels of metoprolol and carvedilol.
* **Bradycardic Agents:** Additive effects with non-dihydropyridine calcium channel blockers (verapamil, diltiazem), digoxin, or amiodarone.
* **Insulin/Sulfonylureas:** May mask signs of hypoglycemia.
## Monitoring
Heart rate (target >50–60 bpm), blood pressure, presence of edema or weight gain (in HFrEF), and blood glucose if diabetic.
## Clinical Pearls
* **Cardioselectivity:** β1-selective agents (metoprolol, bisoprolol, atenolol) are preferred in patients with mild COPD/asthma at low doses, though extreme caution is still required.
* **HF Benefit:** Only bisoprolol, carvedilol, and metoprolol succinate are FDA-approved for heart failure.
* **Tapering:** Never stop abruptly; titrate down over 1–2 weeks to avoid rebound sympathetic surge.
* **Vasodilation:** Carvedilol and nebivolol provide additional vasodilatory effects (alpha-1 blockade or nitric oxide release).
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**Educational Disclaimer:** This information is for educational purposes only. Drug dosing, contraindications, and interaction profiles can change. Always verify current prescribing information using official resources (e.g., Lexicomp, Micromedex, or the package insert) before clinical application.
