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# Beta-blockers ## Overview Beta-blockers (beta-adrenergic receptor antagonists) inhibit the sympathetic nervous system by blocking catecholamine binding to beta-receptors. They are classified by cardioselectivity ($\beta_1$ vs. non-selective $\beta_1/\beta_2$), intrinsic sympathomimetic activity, and vasodilatory properties (mixed $\alpha/\beta$ blockade). ## Primary Indications * Hypertension * Heart failure (HFrEF) * Post-myocardial infarction * Angina pectoris * Atrial fibrillation/flutter (rate control) * Thyrotoxicosis (symptom management) * Essential tremor (propranolol) * Migraine prophylaxis (propranolol, timolol) ## Adult Dosing *Dosing varies significantly by indication; consult specific guidelines (e.g., ACC/AHA).* * **Metoprolol Succinate (ER):** Start 12.5–25 mg daily. Target dose for HF: 200 mg daily. * **Carvedilol:** Start 3.125 mg BID. Target dose for HF: 25 mg BID (or 50 mg BID if >85 kg). * **Bisoprolol:** Start 1.25–2.5 mg daily. Target dose for HF: 10 mg daily. * **Propranolol (Immediate Release):** 40–160 mg daily in 2–4 divided doses for hypertension/angina. * **Atenolol:** 25–100 mg daily (Note: Evidence for mortality benefit in HF is poor; generally avoided as first-line for HF). ## Pediatric Dosing *Consult institutional protocols or PALS/BNF for Children guidelines as age/weight-based adjustments are critical.* * **Propranolol:** Hypertension: Initial 0.5–1 mg/kg/day divided BID-QID (Max: 8 mg/kg/day). * **Atenolol:** Hypertension: Initial 0.5–1 mg/kg/day (Max: 2 mg/kg/day). * **Metoprolol:** Hypertension: Initial 1 mg/kg/day (Max: 6 mg/kg/day). ## Dose Adjustments * **Renal Impairment:** Atenolol and bisoprolol require dose reduction/longer intervals. Lipophilic agents (metoprolol, carvedilol, propranolol) are heavily hepatic-cleared and typically do not require renal adjustment. * **Hepatic Impairment:** Reduce dosages for propranolol and labetalol due to extensive first-pass metabolism. ## Contraindications * Cardiogenic shock * Sinus bradycardia (generally <50–60 bpm) * Second- or third-degree heart block (without a pacemaker) * Severe reactive airway disease (asthma/COPD) – *caution with non-selective agents* * Decompensated heart failure (unless stable and initiated carefully) ## Adverse Effects * Bradycardia and AV block * Hypotension * Fatigue and exercise intolerance * Bronchospasm (non-selective) * Masking of hypoglycemia symptoms (except diaphoresis) * Peripheral vasoconstriction (cold extremities) * Depression/sleep disturbances ## Key Drug Interactions * **CYP2D6 Inhibitors (e.g., fluoxetine, bupropion):** Increase concentrations of metoprolol and carvedilol. * **Non-dihydropyridine CCBs (verapamil, diltiazem):** Synergistic effects on AV conduction; severe bradycardia/heart block risk. * **Diabetes Medications:** May mask hypoglycemic tachycardia/tremor. * **Clonidine:** Risk of rebound hypertension upon abrupt withdrawal if taken concomitantly. ## Monitoring * Heart rate (before every dose in titration phase). * Blood pressure. * Blood glucose in patients with diabetes. * Monitor for signs of worsening heart failure (weight gain, edema, dyspnea). ## Clinical Pearls * **Acute Withdrawal:** Never stop abruptly; taper over 1–2 weeks to prevent rebound hypertension or tachycardia. * **Selectivity:** Use $\beta_1$-selective agents (metoprolol, bisoprolol, atenolol, nebivolol) in patients with mild asthma or COPD to minimize bronchoconstriction. * **Heart Failure Initiation:** Always start "low and go slow" in patients with reduced ejection fraction to avoid acute decompensation. * **Nebivolol:** Offers unique nitric oxide-mediated vasodilation. *** **Disclaimer:** This information is for educational purposes only. Always consult current clinical guidelines, FDA-approved prescribing information, and your institutional pharmacy protocols before making changes to medication therapy.