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# Beta-Blockers
## Overview
Beta-adrenergic blocking agents competitively antagonize catecholamine binding to beta-receptors. They are categorized as non-selective (e.g., propranolol), beta-1 selective (e.g., metoprolol, atenolol, bisoprolol), or vasodilatory/mixed alpha-beta blockers (e.g., carvedilol, labetalol).
## Primary Indications
Hypertension, stable angina, heart failure with reduced ejection fraction (HFrEF), post-myocardial infarction (MI), tachyarrhythmias, and migraine prophylaxis (propranolol).
## Adult Dosing
* **Metoprolol Succinate:** Start 25–50 mg daily. Max 400 mg/day.
* **Metoprolol Tartrate:** 25–100 mg twice daily.
* **Carvedilol:** Start 3.125–6.25 mg twice daily (HFrEF). Max 25 mg BID (if weight <85kg) or 50 mg BID (if weight >85kg).
* **Bisoprolol:** 2.5–5 mg daily. Max 20 mg/day.
* **Propranolol (Immediate Release):** 40 mg twice daily. Max 320 mg/day.
## Pediatric Dosing
* **Propranolol:** Hypertension: 0.5–1 mg/kg/day divided twice daily. Max 2–4 mg/kg/day.
* **Atenolol:** Hypertension: 0.5–1 mg/kg/day (once daily). Max 100 mg/day.
* **Labetalol:** Hypertension: 1–3 mg/kg/day divided twice daily.
* *Note: Pediatric dosing should always be verified against weight-based institutional protocols or Lexicomp/Pediatric Dosage Handbook.*
## Dose Adjustments
* **Renal Impairment:** Atenolol and nadolol require significant dose reduction or increased intervals. Metoprolol and carvedilol generally require no formal adjustment.
* **Hepatic Impairment:** Reduce starting doses for drugs with high first-pass metabolism (e.g., propranolol, carvedilol).
## Contraindications
Second- or third-degree heart block (without a pacemaker), severe bradycardia, cardiogenic shock, and uncompensated heart failure. Use with extreme caution in active reactive airway disease (bronchospasm) and severe peripheral vascular disease.
## Adverse Effects
Bradycardia, hypotension, fatigue, dizziness, sexual dysfunction, and mask-like symptoms of hypoglycemia in diabetic patients. Abrupt withdrawal may cause rebound tachycardia or hypertensive crisis.
## Key Drug Interactions
* **CYP2D6 Inhibitors (e.g., fluoxetine, paroxetine):** Increase levels of metoprolol and carvedilol.
* **Non-DHP CCBs (diltiazem, verapamil):** Potentiation of bradycardia and AV block.
* **Insulin/Sulfonylureas:** Masking of hypoglycemic awareness (tachycardia/tremor).
## Monitoring
Blood pressure and heart rate (target HR usually 55–60 bpm). Monitor glucose in patients with diabetes and lung function in susceptible patients.
## Clinical Pearls
* **Selective vs. Non-selective:** Use beta-1 selective agents in patients with mild-to-moderate pulmonary disease to minimize bronchoconstriction.
* **Heart Failure:** Only carvedilol, metoprolol succinate, and bisoprolol are established for stable HFrEF mortality reduction.
* **Titration:** Always "start low and go slow" in heart failure to prevent decompensation.
* **Lipophilicity:** Lipophilic agents (propranolol) cross the blood-brain barrier more readily, which may increase CNS-related side effects (e.g., nightmares, depression).
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**Educational Disclaimer:** This information is for educational purposes only and does not constitute medical advice. Clinical protocols vary; always verify current prescribing information, contraindications, and laboratory requirements via institutional policy, the manufacturer’s package insert, or primary drug databases (e.g., Lexicomp, UpToDate) before prescribing or administering medication.
