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# Beta Blockers ## Overview Beta-adrenergic blocking agents competitively antagonize catecholamines at beta-1 (cardiac) and/or beta-2 (bronchial/vascular) receptors. They are categorized by selectivity (cardioselective vs. non-selective) and intrinsic sympathomimetic activity (ISA). Common examples include Metoprolol (selective), Propranolol (non-selective), and Carvedilol (mixed alpha/beta). ## Primary Indications * Hypertension * Heart failure with reduced ejection fraction (HFrEF) * Post-myocardial infarction (MI) * Tachyarrhythmias (e.g., AFib rate control) * Angina pectoris * Migraine prophylaxis (propranolol) * Portal hypertension (nadolol/propranolol) ## Adult Dosing *Dosing varies widely by agent and indication. Follow institutional protocols; typical examples:* * **Metoprolol Succinate (ER):** Start 25–50 mg daily; titrate every 1–2 weeks. Max: 200 mg/day. * **Carvedilol:** Start 3.125 mg BID for HFrEF. Target dose: 25 mg BID (or 50 mg BID if >85 kg). * **Propranolol (Migraine):** Start 40–80 mg daily in divided doses. Max: 240 mg/day. * **Atenolol:** 25–100 mg daily for hypertension. ## Pediatric Dosing *Utilize weight-based dosing; significant inter-patient variability exists.* * **Propranolol:** 0.5–4 mg/kg/day divided BID–QID (varies by indication). * **Atenolol:** 0.5–1 mg/kg/dose once daily. * **Esmolol (IV for urgent tachycardia):** Loading dose 100–500 mcg/kg over 1 minute; infusion 25–300 mcg/kg/min. ## Dose Adjustments * **Renal Impairment:** Atenolol and Nadolol require significant renal adjustment or avoidance. Lipophilic agents (Metoprolol, Propranolol) are hepatic-cleared and generally require less adjustment. * **Hepatic Impairment:** Reduce starting doses for agents extensively metabolized by the liver (e.g., Propranolol, Carvedilol). ## Contraindications * Second or third-degree heart block (without a pacemaker). * Severe bradycardia (typically <50–60 bpm). * Decompensated heart failure (unless stable and optimized). * Cardiogenic shock. * Severe reactive airway disease (asthma/COPD) for non-selective agents. ## Adverse Effects * Bradycardia and heart block. * Hypotension. * Fatigue, dizziness, or drowsiness. * Masking of hypoglycemia symptoms (except sweating). * Bronchospasm (primarily non-selective). * Sexual dysfunction. * Cold extremities (Raynaud’s phenomenon). ## Key Drug Interactions * **Digoxin/Non-dihydropyridine CCBs (Diltiazem, Verapamil):** Additive bradycardia; monitor heart rate closely. * **CYP2D6 Inhibitors:** May significantly increase serum concentrations of Metoprolol and Carvedilol. * **Insulin/Sulfonylureas:** Beta-blockers may mask tachycardia during hypoglycemia and delay recovery from hypoglycemic events. ## Monitoring * Heart rate and blood pressure (pre-dose). * ECG for PR interval and conduction changes. * Blood glucose in patients with diabetes. * Signs of peripheral edema or exacerbation of heart failure. ## Clinical Pearls * **Do not abruptly discontinue:** Always taper over 1–2 weeks to prevent rebound hypertension, tachycardia, or ischemia. * **Cardioselectivity:** Selectivity for beta-1 receptors is relative and dose-dependent; "cardioselective" agents may still cause bronchospasm at high doses. * **Lipophilicity:** More lipophilic agents (e.g., Propranolol) cross the blood-brain barrier more easily, increasing the risk of CNS side effects (vivid dreams, insomnia). *** **Educational Disclaimer:** This information is for educational purposes only. Drug dosing, contraindications, and interactions must be verified against current institutional protocols, prescribing leaflets, and clinical decision support tools (e.g., Lexicomp, UpToDate) prior to administration. Professional clinical judgment is required.