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# Beta Blockers ## Overview Beta-adrenergic blocking agents competitively antagonize catecholamine binding to beta-receptors. Agents are classified by receptor selectivity (β1-selective vs. non-selective) and intrinsic sympathomimetic activity (ISA). Common examples include Metoprolol (β1 selective), Carvedilol (non-selective, α1-blocking), and Propranolol (non-selective). ## Primary Indications * **Cardiovascular:** Hypertension, chronic heart failure (HFrEF), post-myocardial infarction, angina pectoris, supraventricular/atrial arrhythmias. * **Non-cardiac:** Migraine prophylaxis (propranolol), essential tremor, thyrotoxicosis, portal hypertension (variceal bleeding prophylaxis). ## Adult Dosing * **Metoprolol Succinate (ER):** Start 25–50 mg daily. Max: 400 mg/day for hypertension/angina. Titrate slowly in HFrEF. * **Carvedilol:** Start 3.125 mg BID. Target: 25 mg BID (weight <85kg) or 50 mg BID (weight >85kg) for HFrEF. * **Propranolol (Migraine):** Start 40–80 mg daily in divided doses. Max: 240 mg/day. * *Note: Dosing is highly indication-specific; refer to institutional guidelines for titration schedules.* ## Pediatric Dosing * **Propranolol:** 0.5–2 mg/kg/day divided BID–QID (varies by condition, e.g., hypertension, infantile hemangioma). * **Atenolol:** 0.5–1 mg/kg/day once daily. * *Note: Pediatric dosing requires weight-based calculation and careful titration. Always verify against pediatric-specific formularies (e.g., Lexicomp/Harriet Lane).* ## Dose Adjustments * **Renal:** Atenolol, Nadolol, and Bisoprolol require reduction in severe renal impairment (CrCl <30 mL/min). Metoprolol and Carvedilol generally do not require adjustment. * **Hepatic:** Propranolol and Carvedilol require cautious dosing/reduction in severe hepatic impairment due to high first-pass metabolism. ## Contraindications * Second- or third-degree heart block (without a pacemaker). * Severe bradycardia (typically <50-60 bpm). * Decompensated heart failure (unless stable). * Cardiogenic shock. * Severe reactive airway disease (non-selective agents). ## Adverse Effects * **Common:** Bradycardia, hypotension, fatigue, dizziness, sexual dysfunction. * **Metabolic:** Masking of hypoglycemia symptoms (except sweating), impaired glucose tolerance. * **Pulmonary:** Bronchospasm (caution with non-selective agents in asthma/COPD). * **Withdrawal:** Abrupt cessation may trigger rebound hypertension or tachycardia. ## Key Drug Interactions * **AV Node Blockers:** Additive effect with nondihydropyridine calcium channel blockers (verapamil, diltiazem) or digitalis glycosides—risk of severe bradycardia. * **CYP450:** Many beta-blockers (e.g., carvedilol, propranolol, metoprolol) are metabolized by CYP2D6; potent inhibitors (fluoxetine, paroxetine) may increase serum concentrations. ## Monitoring * **HR and BP:** Prior to initiation and at every dose adjustment. * **Blood Glucose:** In patients with diabetes mellitus. * **Pulmonary:** Assessment for wheezing in susceptible populations. * **Heart Failure Status:** Monitor for signs of worsening volume overload (edema, weight gain). ## Clinical Pearls * **Beta-1 Selectivity:** Selectivity is relative and decreases at high doses; non-selective agents should be avoided in patients with history of severe asthma. * **Acute MI:** Beta-blockers remain a cornerstone of post-MI care, but initiation should be avoided in unstable patients with signs of pump failure. * **Tapering:** Never withdraw beta-blockers abruptly; taper over 1–2 weeks to avoid catecholamine storm and ischemic events. *** **Educational Disclaimer:** This information is for educational purposes only. Always consult current, reputable clinical resources (e.g., package inserts, Lexicomp, UpToDate, or institutional protocols) before prescribing or administering medication.