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# Beta-Blockers ## Overview Beta-adrenergic blocking agents competitively antagonize catecholamines at beta-1 (cardiac) and/or beta-2 (smooth muscle/bronchial) receptors. Agents are classified by cardioselectivity (e.g., metoprolol is β1-selective), intrinsic sympathomimetic activity (ISA), and vasodilatory properties (e.g., carvedilol/nebivolol). ## 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 *Note: Dosing varies significantly by indication; consult local protocols for specific titration.* * **Metoprolol Succinate (ER):** Start 25–50 mg daily. Max: 400 mg/day. * **Metoprolol Tartrate (IR):** 25–100 mg BID. Max: 400 mg/day (split doses). * **Carvedilol:** 3.125–6.25 mg BID. Max: 50 mg BID (if >85 kg). * **Bisoprolol:** 2.5–5 mg daily. Max: 20 mg/day. * **Propranolol (IR):** 40–160 mg/day in divided doses. Max: 320–480 mg/day. ## Pediatric Dosing *Dosing must be weight-based; always verify via pediatric-specific resources like a Harriet Lane Handbook.* * **Propranolol:** Hypertension: 0.5–1 mg/kg/day divided BID–QID. Max: 8 mg/kg/day. * **Atenolol:** Hypertension: 0.5–1 mg/kg/day. Max: 2 mg/kg/day. * **Metoprolol:** Hypertension: 1–2 mg/kg/day divided BID. Max: 6 mg/kg/day. ## Dose Adjustments * **Hepatic Impairment:** Reduce starting dose for lipophilic agents (e.g., propranolol, carvedilol, metoprolol). * **Renal Impairment:** Generally no adjustment required for lipid-soluble agents; dosage reduction may be necessary for atenolol or nadolol (renally cleared). * **Heart Failure:** Initiate at very low doses and titrate slowly (e.g., every 2 weeks) to prevent acute decompensation. ## Contraindications Second- or third-degree heart block (without a pacemaker), severe bradycardia, cardiogenic shock, uncompensated heart failure, and severe reactive airway disease (non-selective agents). ## Adverse Effects Bradycardia, hypotension, fatigue, dizziness, sexual dysfunction, and masks symptoms of hypoglycemia (except sweating). Abrupt cessation can cause rebound hypertension or tachycardia. ## Key Drug Interactions * **Non-dihydropyridine CCBs (Diltiazem/Verapamil):** Synergistic effects leading to profound bradycardia or heart block. * **CYP2D6 Inhibitors:** May increase serum concentrations of metoprolol or carvedilol. * **Clonidine:** Risk of rebound hypertension if beta-blocker is withdrawn first. ## Monitoring Heart rate (target resting HR 55–70 bpm), blood pressure, presence of peripheral edema, signs of bronchospasm, and blood glucose in patients with diabetes. ## Clinical Pearls * **Cardioselective agents** (Bisoprolol, Atenolol, Metoprolol) are preferred in patients with mild-to-moderate pulmonary disease. * **Carvedilol and Nebivolol** offer vasodilatory properties, providing potential benefits in HFrEF. * **Always taper:** Never discontinue abruptly to avoid cardiac ischemia or hypertensive crisis. * Instruct patients that the "ghost tablet" of metoprolol succinate in the stool is normal (the non-absorbable shell). *** **Educational Disclaimer:** This information is for educational purposes only. Always verify dosages, contraindications, and drug interactions against current local institutional protocols and official prescribing information (package insert) before clinical application.