Alpha Blockers in Pediatric Medicine
Alpha Blockers in Pediatric Medicine
Key Points
- Alpha blockers competitively inhibit α-adrenergic receptors
- Used in various pediatric conditions including hypertension and neurogenic bladder
- Different subtypes target α₁ or α₂ receptors with varying selectivity
- Require careful dose titration and monitoring in children
- Important role in management of pheochromocytoma and neurogenic disorders
Clinical Significance
- First-line therapy for specific conditions
- Valuable adjunctive treatment in resistant hypertension
- Important role in perioperative management
- Significant impact on quality of life in urological conditions
Types & Classification
Selective α₁-Blockers
- Short-Acting
- Prazosin
- Duration: 6-8 hours
- Multiple daily dosing required
- Long-Acting
- Doxazosin
- Terazosin
- Duration: 12-24 hours
- Ultra Long-Acting
- Tamsulosin
- Duration: >24 hours
- Uroselectivity advantage
Non-Selective Alpha Blockers
- Mixed α/β Blockers
- Labetalol
- Carvedilol
- α₁/α₂ Blockers
- Phenoxybenzamine
- Irreversible binding characteristics
Clinical Pharmacology
Mechanism of Action
- Primary Actions
- Competitive inhibition of α₁-receptors
- Reduced vascular smooth muscle tone
- Decreased peripheral vascular resistance
- Bladder neck relaxation (in urological applications)
- Receptor Specificity
- α₁A: Prostate, bladder neck
- α₁B: Vascular smooth muscle
- α₁D: Bladder, spinal cord
Pharmacokinetics in Children
- Absorption
- Variable oral bioavailability
- Food effects on absorption
- Age-dependent variations
- Distribution
- High protein binding
- Good tissue penetration
- Variable volume of distribution
- Metabolism
- Hepatic metabolism (CYP450)
- Age-related clearance differences
- Active metabolites in some drugs
Clinical Indications
Primary Indications
- Hypertension
- Essential hypertension
- Resistant hypertension
- Neurogenic hypertension
- Pheochromocytoma
- Preoperative preparation
- Chronic management
- Crisis management
- Urological Conditions
- Neurogenic bladder
- Bladder neck dysfunction
- Voiding dysfunction
Secondary Applications
- Raynaud's phenomenon
- Autonomic dysfunction
- PTSD-associated nightmares (prazosin)
- Peripheral vascular disorders
Administration & Dosing
Prazosin
- Initial Dose
- 0.01-0.05 mg/kg/dose
- Start at bedtime to minimize first-dose effect
- Maximum initial dose: 1 mg
- Maintenance
- 0.025-0.25 mg/kg/dose TID-QID
- Maximum daily dose: 0.5 mg/kg/day
Doxazosin
- Initial Dose
- 1 mg once daily
- Age >12 years initially
- Titration
- Increase by 1 mg every 1-2 weeks
- Maximum: 4 mg/day in children
Phenoxybenzamine
- Pheochromocytoma Dosing
- Initial: 0.2 mg/kg/day divided BID
- Increase by 0.2 mg/kg/day every 3-4 days
- Maximum: 2 mg/kg/day
Safety & Monitoring
Adverse Effects
- Common Effects
- First-dose hypotension
- Dizziness
- Orthostatic hypotension
- Fatigue
- Nasal congestion
- Serious Concerns
- Syncope
- Priapism (rare)
- Growth effects (monitor)
Monitoring Requirements
- Initial Phase
- Blood pressure monitoring
- Orthostatic measurements
- Heart rate tracking
- First-dose observation
- Long-term Follow-up
- Regular BP checks
- Growth monitoring
- Symptom assessment
- Quality of life evaluation
Special Precautions
- Avoid sudden discontinuation
- Caution with concurrent medications
- Activity modifications
- Surgical considerations
