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# Beta Blockers ## Overview Beta-adrenergic blocking agents (beta-blockers) compete with catecholamines for beta-receptor sites. They are categorized by selectivity (β1-selective vs. non-selective) and intrinsic sympathomimetic activity (ISA). ## Primary Indications * Hypertension * Chronic heart failure (HFrEF) * Atrial fibrillation/flutter rate control * Post-myocardial infarction (secondary prevention) * Angina pectoris * Thyrotoxicosis (adjunct) * Migraine prophylaxis (propranolol) ## Adult Dosing *Dosing is indication-specific; these are common initial/maintenance ranges.* * **Metoprolol Succinate (ER):** Initial 25–50 mg daily; max 400 mg daily. * **Metoprolol Tartrate (IR):** Initial 25–50 mg BID; max 400 mg daily. * **Bisoprolol:** Initial 2.5–5 mg daily; max 20 mg daily. * **Carvedilol:** Initial 3.125–6.25 mg BID; max 25 mg BID (mild-to-moderate HF) or 50 mg BID (post-MI). * **Propranolol:** Hypertension: 40–160 mg daily (divided). ## Pediatric Dosing *Clinical judgment and weight-based calculations are required. Consult local pediatric protocols (e.g., Harriet Lane).* * **Propranolol:** 0.5–1 mg/kg/day divided BID-TID; max 8 mg/kg/day. * **Atenolol:** 0.5–1 mg/kg/day once daily; max 2 mg/kg/day. * **Note:** Use with extreme caution in neonates; risk of hypoglycemia and bradycardia. ## Dose Adjustments * **Renal Impairment:** Generally not required for metoprolol or carvedilol (hepatic clearance). Atenolol and nadolol require significant dose reductions or lengthened dosing intervals in renal failure (CrCl <30 mL/min). * **Hepatic Impairment:** Reduce starting doses for propranolol and carvedilol due to extensive first-pass metabolism. ## Contraindications * Second- or third-degree AV block (without a pacemaker). * Severe bradycardia (typically <50-60 bpm). * Decompensated heart failure (unless stable and supervised). * Cardiogenic shock. * Severe bronchospastic disease (asthma/COPD) for non-selective agents (e.g., propranolol). ## Adverse Effects * **Bradycardia and hypotension.** * **Fatigue and exercise intolerance.** * **Masking signs of hypoglycemia** (e.g., tremors, tachycardia). * **Bronchospasm** (non-selective agents). * **Sexual dysfunction.** * **Cold extremities (Raynaud’s phenomenon).** ## Key Drug Interactions * **Verapamil/Diltiazem:** High risk of synergistic bradycardia and heart block. * **Digoxin:** Additive slowing of AV conduction. * **CYP2D6 Inhibitors (e.g., fluoxetine, paroxetine):** Increases plasma levels of metoprolol and carvedilol. * **Insulin/Sulfonylureas:** May delay recovery from hypoglycemia and mask symptoms. ## Monitoring * **HR and Blood Pressure:** Assess prior to each dose initiation and titration. * **Respiratory status:** Monitor for wheezing in patients with reactive airway disease. * **Blood glucose:** Frequent monitoring in patients with labile diabetes. * **Weight:** In heart failure patients, monitor for signs of fluid retention. ## Clinical Pearls * **Withdrawal:** Never discontinue abruptly; taper over 1–2 weeks to prevent rebound hypertension, tachycardia, or myocardial ischemia. * **Selectivity:** Use β1-selective agents (metoprolol, bisoprolol, atenolol) in patients with mild reactive airway disease, though "cardiospecificity" is dose-dependent and may be lost at higher doses. * **Heart Failure:** Only bisoprolol, carvedilol, and metoprolol succinate are indicated for chronic HFrEF; ensure patients are clinically stable before initiation. *** **Educational Disclaimer:** This information is for educational purposes only. Drug dosing, contraindications, and interactions can change. Always verify current prescribing information using official drug monographs or institutional clinical decision support tools before prescribing or administering medication.