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# Beta-Blockers
## Overview
Beta-adrenergic blocking agents competitively antagonize catecholamines at beta-receptors. They are categorized as non-selective (e.g., propranolol), cardioselective ($\beta_1$-selective, e.g., metoprolol, bisoprolol, atenolol), or mixed $\alpha/\beta$ antagonists (e.g., carvedilol, labetalol).
## Primary Indications
Hypertension, stable angina, heart failure with reduced ejection fraction (HFrEF), post-myocardial infarction (secondary prevention), atrial fibrillation/flutter (rate control), migraine prophylaxis, and essential tremor.
## Adult Dosing
* **Metoprolol Succinate (ER):** Start 25–50 mg daily; titrate to max 200 mg/day.
* **Carvedilol (HFrEF):** Start 3.125 mg BID; titrate to max 25 mg BID (pts $\le$85kg) or 50 mg BID (pts >85kg).
* **Bisoprolol:** Start 2.5–5 mg daily; max 20 mg/day.
* **Propranolol (Migraine):** Start 40 mg BID; titrate to max 240 mg/day.
* *Note: Dosing is highly indication-specific; refer to institutional guidelines for acute vs. chronic management.*
## Pediatric Dosing
*Dosing often weight-based; requires pediatric specialist oversight.*
* **Propranolol (Hypertension):** Start 0.5–1 mg/kg/day divided BID; max 8 mg/kg/day.
* **Atenolol:** 0.5–1 mg/kg/day once daily; max 2 mg/kg/day.
* **Propranolol (Infantile Hemangioma):** 1–3 mg/kg/day divided BID.
## Dose Adjustments
* **Renal Impairment:** Atenolol and nadolol require significant dose reduction or increased intervals. Metoprolol and carvedilol are primarily hepatically metabolized and generally do not require dose adjustment.
* **Hepatic Impairment:** Reduce starting doses for propranolol and carvedilol due to extensive first-pass metabolism.
## Contraindications
Second or third-degree heart block (without a pacemaker), severe bradycardia, cardiogenic shock, and uncompensated heart failure. Use caution in severe reactive airway disease (asthma/COPD) with non-selective agents.
## Adverse Effects
Bradycardia, hypotension, fatigue, dizziness, sexual dysfunction, masking of hypoglycemia symptoms (except sweating), and bronchospasm (non-selective agents).
## Key Drug Interactions
* **CYP2D6 Inhibitors:** (e.g., fluoxetine, paroxetine) increase levels of metoprolol and carvedilol.
* **Bradycardic Agents:** Additive effects with digoxin, non-dihydropyridine calcium channel blockers (verapamil, diltiazem), and amiodarone.
* **Antidiabetic Agents:** May potentiate hypoglycemia and mask tachycardia associated with low blood sugar.
## Monitoring
Heart rate and blood pressure at baseline and after any titration. In HFrEF: monitor for signs of fluid overload (weight gain, worsening dyspnea) during initiation. In COPD/Asthma: monitor for increased wheezing or respiratory effort.
## Clinical Pearls
* **Tapering:** Never discontinue beta-blockers abruptly; this can lead to rebound hypertension, tachycardia, or myocardial ischemia due to receptor upregulation. Taper over 1–2 weeks.
* **Selectivity:** In patients with mild reactive airway disease, cardioselective agents (bisoprolol, metoprolol) are preferred over non-selective agents (propranolol, nadolol).
* **HFrEF:** Only bisoprolol, carvedilol, and metoprolol succinate are evidence-based for mortality reduction in HFrEF.
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*Disclaimer: This information is for educational purposes only. Dosage, indications, and contraindications may vary based on patient-specific factors and local clinical protocols. Always verify current prescribing information via official databases (e.g., Lexicomp, UpToDate) or the drug manufacturer before prescribing or administering medication.*
