Introduction
- Essential medications in pediatric cardiology
- Wide therapeutic applications
- Available in multiple formulations
- Various selectivity profiles for different clinical scenarios
Classification
Selective β1-Blockers
- Atenolol
- Metoprolol
- Bisoprolol
- Advantage: Fewer bronchial and metabolic effects
Non-selective β-Blockers
- Propranolol
- Nadolol
- Carvedilol (also α-blocking properties)
- Note: Greater effect on bronchial tone and metabolism
Special Properties
- Intrinsic sympathomimetic activity (ISA): Pindolol
- Alpha-blocking activity: Carvedilol, Labetalol
- Membrane-stabilizing activity: Propranolol
- Lipophilicity: Affects CNS penetration and half-life
Mechanism of Action
Primary Actions
- Competitive antagonism of β-adrenergic receptors
- Reduction in heart rate and contractility
- Decreased cardiac output
- Reduced renin release
- Antiarrhythmic effects (Class II)
Physiologic Effects
- Negative chronotropic effect
- Negative inotropic effect
- Reduced myocardial oxygen demand
- Antihypertensive effect
- Reduced sympathetic outflow
- Modification of baroreceptor sensitivity
Clinical Indications
Cardiac Indications
- Supraventricular tachycardia
- Hypertrophic cardiomyopathy
- Long QT syndrome
- Tetralogy of Fallot (hypercyanotic spells)
- Marfan syndrome (aortic protection)
- Heart failure (specific agents)
Non-Cardiac Indications
- Portal hypertension
- Thyrotoxicosis
- Migraine prophylaxis
- Essential tremor
- Hemangiomas (propranolol)
Specific Clinical Scenarios
- Post-operative tachycardia
- Chronic heart failure (carvedilol)
- Prevention of aortic dissection
- Anxiety with performance situations
Dosing Guidelines
Propranolol
- Initial: 0.5-1 mg/kg/day divided q6-8h
- Maximum: 4 mg/kg/day up to 640 mg/day
- Hemangioma: Start at 0.5 mg/kg/dose BID
- Available forms: Oral solution, tablets, IV
Metoprolol
- Initial: 0.5-1 mg/kg/day divided q12h
- Maximum: 2 mg/kg/day up to 200 mg/day
- Available forms: Immediate/extended release, IV
Carvedilol
- Initial: 0.05 mg/kg/dose BID
- Target: 0.4-0.8 mg/kg/day divided BID
- Maximum: 25 mg BID
- Note: Slow uptitration essential
Atenolol
- Initial: 0.5 mg/kg/day once daily
- Maximum: 2 mg/kg/day up to 100 mg/day
- Advantage: Once-daily dosing
Monitoring & Safety
Required Monitoring
- Heart rate and blood pressure
- ECG at baseline and follow-up
- Growth parameters
- Blood glucose in diabetic patients
- Exercise tolerance
- Signs of heart failure
Adverse Effects
- Bradycardia
- Hypotension
- Fatigue and exercise intolerance
- Sleep disturbances
- Depression (lipophilic agents)
- Bronchospasm (non-selective agents)
- Hypoglycemia (masking symptoms)
- Cold extremities
Contraindications
- Severe bradycardia
- Heart block (2nd or 3rd degree)
- Cardiogenic shock
- Severe asthma (non-selective agents)
- Severe peripheral vascular disease
- Decompensated heart failure
Special Considerations
- Gradual discontinuation to prevent rebound
- Caution in diabetes (masked hypoglycemia)
- Risk of bronchospasm in reactive airway disease
- Periodic assessment of growth and development
- Monitor for depression with lipophilic agents
Drug Interactions
- Calcium channel blockers (enhanced negative inotropy)
- Antiarrhythmics (additive effects)
- Insulin and oral hypoglycemics
- CYP2D6 inhibitors with metoprolol
- NSAIDs (reduced antihypertensive effect)
Further Reading
