What is the commercially available dose for captopril (an angiotensin-converting enzyme inhibitor) and how should I prepare a 2mg dose, three times a day (TID), for an 18kg pediatric patient with heart failure?

Captopril Dosing and Preparation for Pediatric Heart Failure

Commercially Available Doses

Captopril tablets are commercially available in 12.5 mg, 25 mg, 50 mg, and 100 mg strengths, and you will need to prepare an extemporaneous suspension to achieve a 2 mg dose three times daily for your 18 kg pediatric patient. 1

Preparation of Captopril Suspension

To prepare a captopril suspension for a 2 mg TID dose:

• Crush one 25 mg captopril tablet and dissolve it in 12.5 mL of sterile water to create a 2 mg/mL concentration 1, 2
• Administer 1 mL of this suspension (2 mg) three times daily 3
• This preparation should be made fresh and used within 24-48 hours due to stability concerns 2

Important Preparation Considerations

• The FDA label does not provide specific instructions for pediatric suspension preparation, but hospital pharmacies routinely compound captopril suspensions for pediatric use 1, 2
• Unlicensed liquid captopril formulations show significant bioavailability variability (within-subject variability of 97.5% for maximum plasma concentrations), so consistent preparation methods and close monitoring are essential 2
• Do not use commercially available liquid preparations in young infants if they contain sorbitol as a preservative due to hyperosmolar concerns 4

Dosing Rationale for Your Patient

For an 18 kg child with heart failure, a dose of 2 mg TID (total daily dose of 6 mg or 0.33 mg/kg/day) is appropriate as an initial starting dose:

• Pediatric dosing for heart failure typically ranges from 0.3 to 1.5 mg/kg/day divided into three doses 3
• Starting doses should be conservative (0.3-0.5 mg/kg/day) to minimize hypotension risk, particularly in patients on diuretics 5, 3
• Your proposed dose of 0.33 mg/kg/day falls within the recommended starting range 3, 6

Titration Strategy

After initiating at 2 mg TID, gradually increase the dose based on clinical response:

• Increase by 0.3-0.5 mg/kg/day increments every 1-2 weeks as tolerated 3
• Target maintenance doses typically range from 1.0-2.5 mg/kg/day (18-45 mg/day for your 18 kg patient) divided TID 5, 6
• Maximum pediatric doses can reach up to 3.5 mg/kg/day, though most patients respond to lower doses 5

Critical Monitoring Requirements

Monitor the following parameters closely, especially within the first 5 days after initiation or dose increases:

• Blood pressure before each dose initially—hypotension is the most common adverse effect and typically occurs within 5 days of starting or increasing captopril 3, 6
• Serum creatinine and blood urea nitrogen within 3-5 days of initiation and after each dose increase 3, 6
• Serum potassium and sodium levels, particularly if the patient is on potassium-sparing diuretics 5, 6
• Daily weights and clinical signs of heart failure (respiratory rate, feeding tolerance, edema) 5, 6

Common Pitfalls and How to Avoid Them

Hypotension and renal dysfunction are the primary concerns:

• Hyponatremia (low sodium) at baseline increases the risk of severe hypotension after captopril initiation—correct sodium levels before starting if possible 5
• Patients on high-dose diuretics are at higher risk for first-dose hypotension—consider reducing diuretic dose temporarily when initiating captopril 4, 3
• Stop potassium-sparing diuretics (spironolactone) when starting captopril to reduce hyperkalemia risk 5
• If hypotension occurs, reduce the captopril dose by 50% rather than discontinuing entirely 3
• Renal insufficiency that develops is usually reversible with dose reduction or temporary cessation 3, 6

Concomitant Therapy

Captopril should be used in conjunction with:

• Diuretics (furosemide) for volume management—continue at current dose unless patient is hypovolemic 4, 3
• Digoxin may be continued if already prescribed, though its benefit in pediatric heart failure with left-to-right shunts is controversial 4
• Do NOT use potassium-sparing diuretics concurrently due to hyperkalemia risk 5

Expected Clinical Response

Improvement should be evident within 2-4 weeks:

• Increased weight gain (mean improvement from -7 g/day to +13 g/day in one study) 5
• Decreased respiratory rate (mean decrease from 68 to 60 breaths/minute) 5, 6
• Improved feeding tolerance and decreased heart rate 5
• These benefits typically persist long-term without tolerance development 3