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# Beta-blockers ## Overview Beta-blockers (beta-adrenergic antagonists) competitively block catecholamine binding to beta-receptors. They are categorized by selectivity (beta-1 vs. non-selective) and intrinsic sympathomimetic activity (ISA). Common examples include Metoprolol (selective), Propranolol (non-selective), and Carvedilol (non-selective with alpha-1 blockade). ## Primary Indications * Hypertension * Heart failure with reduced ejection fraction (HFrEF) * Post-myocardial infarction (MI) * Atrial fibrillation/flutter rate control * Angina pectoris * Migraine prophylaxis (propranolol) * Essential tremor (propranolol) ## Adult Dosing * **Metoprolol Succinate (ER):** Start 25–50 mg daily; titrate every 1–2 weeks to max 200 mg/day (HFrEF target). * **Metoprolol Tartrate:** 25–100 mg twice daily; max 400 mg/day (rarely used for HFrEF). * **Carvedilol (IR):** Start 3.125 mg twice daily; titrate every 2 weeks to max 25 mg twice daily (<85kg) or 50 mg twice daily (>85kg) for HFrEF. * **Atenolol:** 25–50 mg once daily; max 100 mg/day. * **Propranolol (IR):** 40 mg twice daily; titrate as needed for hypertension; max 320–480 mg/day. ## Pediatric Dosing *Dosing is highly dependent on institutional protocol, weight, and indication.* * **Propranolol:** Hypertension: 0.5–1 mg/kg/day divided twice daily; max 8 mg/kg/day. * **Atenolol:** Hypertension: 0.5–1 mg/kg/dose once daily; max 2 mg/kg/day. * **Metoprolol:** Hypertension: 1–2 mg/kg/day divided twice daily; max 6 mg/kg/day. ## Dose Adjustments * **Hepatic Impairment:** Reduce dose for drugs with extensive first-pass metabolism (e.g., Propranolol, Carvedilol). * **Renal Impairment:** Generally unnecessary for lipophilic agents (Metoprolol). Atenolol (renally cleared) may require dose reductions. ## Contraindications * Second or third-degree heart block (without a pacemaker). * Severe bradycardia (typically <50 bpm) or symptomatic hypotension. * Decompensated heart failure (unless stable). * Severe reactive airway disease (e.g., severe asthma); use cardioselective agents with extreme caution. * Cardiogenic shock. ## Adverse Effects * **Cardiovascular:** Bradycardia, hypotension, exacerbation of heart failure. * **Metabolic:** Masking of hypoglycemia symptoms (except sweating), potentially adverse lipid profiles. * **CNS:** Fatigue, vivid dreams, depression. * **Respiratory:** Bronchospasm (primarily non-selective agents). ## Key Drug Interactions * **CYP2D6 Inhibitors (e.g., Fluoxetine, Paroxetine):** Increase concentrations of Metoprolol and Carvedilol. * **AV Node Agents (e.g., Verapamil, Diltiazem, Digoxin):** Increased risk of profound bradycardia and heart block. * **Insulin/Sulfonylureas:** Masking of tachycardia as a warning sign of hypoglycemia. ## Monitoring * Heart rate and blood pressure (at initiation and during titration). * Cardiac rhythm (ECG for blocks). * Blood glucose in patients with diabetes. * Pulmonary status in patients with comorbid asthma/COPD. ## Clinical Pearls * **Do not abruptly discontinue:** Always taper over 1–2 weeks to prevent rebound hypertension or tachycardia. * **Metoprolol conversion:** Metoprolol Succinate (ER) and Tartrate are NOT bioequivalent; Succinate is preferred for HFrEF. * **Lipophilicity:** More lipophilic agents (Propranolol) cross the blood-brain barrier easily, resulting in higher risk of CNS side effects (e.g., vivid dreams). * *Note:* Target doses for HFrEF should ideally reach evidence-based clinical trial doses whenever tolerated. *** **Disclaimer:** This information is for educational purposes only. Always consult current, evidence-based clinical databases (e.g., UpToDate, Lexicomp) and institutional protocols before prescribing or administering any medication.