Key Points
- Vasodilators are essential medications that increase blood vessel diameter by relaxing vascular smooth muscle
- Primary use in pediatric hypertension, heart failure, and pulmonary hypertension
- Mechanism involves either direct smooth muscle relaxation or endothelial-mediated vasodilation
- Dosing requires careful consideration of age, weight, and underlying condition
Classification of Pediatric Vasodilators
- Direct-acting:
- Hydralazine (0.1-0.5 mg/kg/dose)
- Minoxidil (0.1-1 mg/kg/day)
- Nitric oxide donors:
- Sodium nitroprusside (0.3-10 μg/kg/min)
- Nitroglycerin (0.1-10 μg/kg/min)
Direct-Acting Vasodilators
Hydralazine
Clinical Pharmacology
- Mechanism: Direct arteriolar smooth muscle relaxation
- Onset: 20-30 minutes oral, 10-20 minutes IV
- Duration: 4-6 hours
Dosing Guidelines
- Initial: 0.1-0.2 mg/kg/dose
- Maximum single dose: 25 mg
- Frequency: Every 6-8 hours
- Maximum daily dose: 7.5 mg/kg/day up to 200 mg daily
Minoxidil
Clinical Pharmacology
- Mechanism: K+ channel activation leading to membrane hyperpolarization
- Onset: 30 minutes to 2 hours
- Duration: 24 hours
Dosing Guidelines
- Initial: 0.1-0.2 mg/kg/day divided BID-TID
- Titration: Increase by 0.1-0.2 mg/kg/day every 3 days
- Maximum daily dose: 50 mg/day
Nitric Oxide Donors
Sodium Nitroprusside
Clinical Pharmacology
- Mechanism: NO release leading to cGMP-mediated vasodilation
- Onset: Immediate
- Duration: 1-10 minutes after discontinuation
Clinical Use Guidelines
- Initial rate: 0.3 μg/kg/min
- Titration: Increase by 0.5 μg/kg/min every 5-10 minutes
- Maximum rate: 10 μg/kg/min
- Duration: Limited to 72 hours due to thiocyanate toxicity risk
Nitroglycerin
Clinical Pharmacology
- Mechanism: NO donation leading to venous and arterial dilation
- Onset: 1-2 minutes
- Duration: 3-5 minutes
Clinical Use Guidelines
- Initial rate: 0.1-0.2 μg/kg/min
- Titration: Increase by 0.2-0.5 μg/kg/min every 5-10 minutes
- Maximum rate: 10 μg/kg/min
Clinical Applications
Primary Indications
- Hypertensive Emergency
- First-line: Sodium nitroprusside
- Alternative: IV hydralazine
- Target: Gradual BP reduction over 24-48 hours
- Chronic Hypertension
- Oral hydralazine: Mild to moderate HTN
- Minoxidil: Resistant hypertension
- Heart Failure
- Acute: Nitroglycerin for preload reduction
- Chronic: Oral vasodilators as part of combination therapy
Special Considerations
- Neonatal period requires careful dose adjustment
- Congenital heart disease may alter response
- Renal impairment affects drug clearance
Adverse Effects and Precautions
Common Adverse Effects
- Hydralazine
- Tachycardia
- Fluid retention
- Lupus-like syndrome
- Headache
- Minoxidil
- Hypertrichosis
- Sodium retention
- Pericardial effusion
- Sodium Nitroprusside
- Thiocyanate toxicity
- Methemoglobinemia
- Rebound hypertension
Risk Mitigation
- Regular monitoring of blood pressure
- Electrolyte balance assessment
- Thiocyanate levels for prolonged nitroprusside use
- ECG monitoring in acute settings
Monitoring and Follow-up
Initial Assessment
- Baseline vital signs
- Complete blood count
- Renal function tests
- Electrolytes
- ECG
Ongoing Monitoring
- Acute Setting
- Continuous BP monitoring
- Cardiac monitoring
- Fluid status
- Hourly urine output
- Chronic Management
- BP checks every 2-4 weeks initially
- Monthly labs for first 3 months
- Growth monitoring in children
Further Reading
