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# Beta Blockers
## Overview
Beta-adrenergic blocking agents competitively antagonize catecholamines at beta-adrenergic receptors. They are classified by receptor selectivity (Beta-1 selective vs. non-selective) and intrinsic sympathomimetic activity (ISA). Common examples include Metoprolol (selective), Atenolol (selective), and Propranolol (non-selective).
## Primary Indications
Hypertension, stable angina pectoris, arrhythmias (e.g., AFib rate control), heart failure with reduced ejection fraction (HFrEF), and post-myocardial infarction. Off-label uses include anxiety, migraine prophylaxis, and essential tremor.
## Adult Dosing
* **Metoprolol Succinate (ER):** Start 25–50 mg daily; titrate every 1–2 weeks. Max: 400 mg/day.
* **Metoprolol Tartrate (IR):** 25–100 mg twice daily. Max: 450 mg/day.
* **Carvedilol (Non-selective/Alpha-blocker):** 3.125 mg twice daily; titrate every 2 weeks. Max: 25 mg BID (<85 kg) or 50 mg BID (>85 kg) for HFrEF.
* **Propranolol (IR):** 40 mg twice daily. Max: 320 mg/day (varies by indication).
* **Atenolol:** 25–50 mg once daily. Max: 100 mg/day.
*Note: Specific titration targets vary significantly by local protocol and clinical indication.*
## Pediatric Dosing
Dosing is highly indication-dependent and weight-based.
* **Propranolol (Hypertension/Arrhythmia):** 0.5–1 mg/kg/day divided BID-TID; range 0.5–4 mg/kg/day.
* **Atenolol:** 0.5–1 mg/kg/dose once daily.
* **Metoprolol:** Consider 1–2 mg/kg/day divided BID.
* *Consult institutional neonatal/pediatric handbooks (e.g., Harriet Lane) for specific ages and weight-based calculations.*
## Dose Adjustments
* **Renal Impairment:** Atenolol requires dose reduction; lipophilic agents (e.g., Metoprolol, Propranolol) are hepatically cleared and generally do not require dose adjustment.
* **Hepatic Impairment:** Use caution; dose reduction may be required for agents with high first-pass metabolism (e.g., Propranolol).
* **Elderly:** Start at the lower end of the dosing range to prevent bradycardia and hypotension.
## Contraindications
Second- or third-degree heart block (without a pacemaker), severe bradycardia, cardiogenic shock, and decompensated heart failure. Use with extreme caution in patients with severe reactive airway disease (e.g., uncontrolled asthma, severe COPD), though Beta-1 selective agents are often tolerated.
## Adverse Effects
Bradycardia, hypotension, fatigue, dizziness, sexual dysfunction, cold extremities, and bronchospasm. Can mask hypoglycemic symptoms (except sweating) in patients with diabetes.
## Key Drug Interactions
* **CYP2D6 Inhibitors:** (e.g., Fluoxetine, Paroxetine) increase levels of Metoprolol and Carvedilol.
* **Negative Chronotropes:** Concurrent use of non-dihydropyridine calcium channel blockers (Verapamil, Diltiazem) significantly increases risk of heart block or profound bradycardia.
* **Digoxin:** Additive effect on slowing AV node conduction.
## Monitoring
Monitor blood pressure and heart rate (target HR usually 55–60 bpm). Assess for peripheral edema, weight gain, or shortness of breath (HF worsening). Monitor blood glucose in patients with insulin-dependent diabetes.
## Clinical Pearls
* **Abrupt Withdrawal:** Never stop abruptly; this can lead to rebound hypertension or tachycardia due to receptor up-regulation. Taper over 1–2 weeks.
* **Masking Hypoglycemia:** Non-selective beta-blockers pose a higher risk; advise diabetic patients to monitor for symptoms other than palpitations/shakiness (e.g., sweating).
* **Formulation:** Metoprolol Succinate (ER) is preferred for HFrEF; IR versions have not demonstrated the same mortality benefits.
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**Educational Disclaimer:** This information is for educational purposes only. Clinical practice guidelines shift frequently. Always verify the current prescribing information via a reliable drug database (e.g., Lexicomp, Clinical Pharmacology) or your institutional pharmacy formulary before prescribing or administering medication.
