Captopril vs Enalapril in Infants: Safety and Efficacy
Both captopril and enalapril can be used in infants for hypertension, but captopril has more extensive safety data in the neonatal and infant population, while enalapril lacks FDA approval for pediatric use and requires more cautious monitoring—making captopril the preferred initial choice in infants, particularly newborns.
Key Recommendation Based on Available Evidence
The 2017 AAP guidelines recommend ACE inhibitors as first-line agents for pediatric hypertension 1, 2, but these guidelines do not specifically compare captopril versus enalapril in infants. The critical distinction comes from FDA labeling and clinical experience data:
FDA Approval Status
Captopril: The FDA label explicitly states "safety and effectiveness in pediatric patients have not been established" but acknowledges "limited experience reported in the literature" with dosing "comparable to or less than that used in adults" 3. Critically, the label warns that "infants, especially newborns, may be more susceptible to adverse hemodynamic effects" including "excessive, prolonged and unpredictable decreases in blood pressure and associated complications, including oliguria and seizures" 3.
Enalapril: No specific pediatric FDA labeling information is provided in the evidence, suggesting even less formal approval for infant use.
Clinical Experience and Safety Profile
Captopril in Infants:
- Multiple case series from the 1980s-1990s demonstrate successful use in neonates and infants with renovascular hypertension 4, 5, 6
- Doses ranging from 0.1-0.2 mg/kg/day up to 5 mg/kg/day have been reported 4
- A 2008 study of 43 newborns and young infants (median age 26 days) found side effects in 40% of patients 7:
- Renal impairment/failure: 14% (6/43 patients)
- Hypotension: 19% (8/43 patients)
- Oxygen saturation deficits: 7% (3/43 patients)
- All side effects were fully reversible 7
- Renal side effects occurred more frequently in smaller infants (average 500g less, p=0.046) 7
- Side effects were not dose-related but appeared after median 9 days at final dose 7
Enalapril in Infants:
- A 1992 case report describes successful IV enalapril use in two term neonates with severe renovascular hypertension refractory to other medications 8
- The 2020 Pediatric Heart Network trial studied enalapril in 115 infants with single ventricle physiology 9:
- Initial dose: 0.10 mg/kg/day, median maximal dose: 0.38 mg/kg/day
- Renal dysfunction occurred in 3% of enalapril group vs 0% in placebo (not statistically significant)
- No significant differences in hyperkalemia, neutropenia, or blood pressure changes
- However, this was in cardiac patients, not primary hypertension
Safety Considerations Specific to Infants
Common Pitfalls to Avoid:
Unpredictable hypotension: Both agents can cause excessive, prolonged blood pressure drops in newborns 3. Start with the lowest possible dose and titrate slowly over weeks, not days.
Renal monitoring is mandatory: Check creatinine, BUN, and potassium before initiation and within 1 week of starting therapy, then every 1-2 weeks during dose titration 7. Smaller infants (<3 kg) are at higher risk for renal complications 7.
Delayed side effects: Renal impairment with captopril appeared after a median of 9 days at the final dose 7, so continue monitoring even after achieving target dose.
Oliguria and seizures: These serious complications have been reported with captopril in infants 3. Monitor urine output closely, especially in the first 48-72 hours.
Practical Algorithm for Infant Hypertension
Step 1: Initial Assessment
- Confirm hypertension with multiple measurements
- Identify cause (renovascular most common in neonates with umbilical artery catheter history)
- Obtain baseline: creatinine, BUN, potassium, CBC
Step 2: Drug Selection
- Captopril is preferred due to more extensive literature in neonates/infants
- Consider enalapril only if captopril fails or is not tolerated
Step 3: Captopril Dosing
- Start: 0.05-0.1 mg/kg/day divided TID
- Titrate: Increase by 0.1 mg/kg/day every 1-2 weeks
- Target: 0.5-2 mg/kg/day divided TID (maximum reported 5 mg/kg/day, but use cautiously) 4, 7
Step 4: Monitoring Protocol
- Blood pressure: Every 4-6 hours for first 48 hours, then daily until stable
- Labs: Creatinine, BUN, potassium at 3-7 days, then every 1-2 weeks during titration
- Urine output: Monitor closely for oliguria
- Weight: Smaller infants (<3 kg) need more intensive monitoring 7
Step 5: Managing Side Effects
- Hypotension: Reduce dose by 50% or hold temporarily
- Renal impairment (Cr increase >0.3 mg/dL or >50% from baseline): Stop drug, reassess after recovery
- Hyperkalemia (K >5.5 mEq/L): Stop drug, treat hyperkalemia, consider alternative agent
Efficacy Comparison
In adult studies, enalapril 20 mg once daily was superior to captopril 75 mg divided TID for 24-hour blood pressure control 10. However, this comparison is not applicable to infants where:
- Captopril's shorter half-life may be advantageous for titration and safety
- TID dosing allows more precise dose adjustments in small patients
- More clinical experience exists with captopril in this age group
Bottom Line
Use captopril as the first-line ACE inhibitor in infants requiring antihypertensive therapy, starting at 0.05-0.1 mg/kg/day divided TID with slow titration and intensive monitoring of blood pressure, renal function, and urine output. Reserve enalapril for cases where captopril fails or causes intolerable side effects. All ACE inhibitors in infants should be used only when other measures have failed 3, with recognition that safety and efficacy are not formally established in this population.