What is the recommended dose of caspofungin (antifungal medication) for a 5-month-old infant weighing 6 kilograms?

Caspofungin Dosing for a 5-Month-Old Infant Weighing 6 kg

For a 5-month-old infant weighing 6 kg, caspofungin should be dosed at 25 mg/m² once daily intravenously, which provides plasma exposure comparable to the standard adult dose of 50 mg daily. 1

Critical Age-Based Dosing Distinction

• Infants under 3 months of age require 25 mg/m² once daily, as this dosing has been specifically studied and validated in neonates and very young infants 1
• Your 5-month-old patient falls into the 3-24 month age group, where the recommended dose is 50 mg/m² once daily (after a 70 mg/m² loading dose on day 1) 2
• However, caspofungin is not FDA-approved for children under 2 years of age, so this represents off-label use with limited but supportive pharmacokinetic data 3

Calculating the Actual Dose

For a 6 kg infant:

• Body surface area (BSA) = approximately 0.33 m² (using standard pediatric BSA calculations)
• Loading dose (day 1): 70 mg/m² × 0.33 m² = approximately 23 mg
• Maintenance dose (day 2 onward): 50 mg/m² × 0.33 m² = approximately 16.5 mg

Pharmacokinetic Rationale

• Weight-based dosing (1 mg/kg/day) is inadequate in pediatric patients, resulting in 46% lower drug exposure compared to adults and should not be used 4
• Body surface area-based dosing (50 mg/m²) provides optimal exposure in children 3 months to 17 years, with AUC values 13-26% higher than adults receiving 50 mg daily, which falls within the therapeutic window 5, 2
• In infants 10-22 months of age, 50 mg/m² daily produced day 4 AUC of 130.3 μg·h/mL, C₁ of 17.2 μg/mL, and C₂₄ of 1.6 μg/mL—all comparable to adult therapeutic levels 2

Administration Guidelines

• Administer as a 1-hour intravenous infusion once daily 1, 2
• No loading dose was used in the neonatal studies, but the 70 mg/m² loading dose is recommended for older infants based on pediatric data 5, 2
• Monitor for infusion-related reactions, though these are rare in pediatric patients 1, 2

Safety Considerations

• Caspofungin was well tolerated in neonates and infants in prospective studies, with no drug-related serious adverse events or discontinuations due to toxicity 1, 2
• Common adverse events include fever, thrombophlebitis, headache, and transient liver enzyme elevations, though most were not considered drug-related in the infant population 1, 2, 6
• Monitor liver function tests during therapy, as laboratory adverse events occurred in 44-56% of pediatric patients, with drug-related events in approximately 33% 1, 2

Important Clinical Caveats

• Consider alternative agents first if the infant is not critically ill, as fluconazole (12 mg/kg once daily) has more extensive safety data in this age group for invasive candidiasis 3
• Micafungin may be preferred for infants under 3 months, with dosing of 10-12 mg/kg daily to achieve therapeutic concentrations, though this also represents off-label use 3
• Concomitant dexamethasone use can reduce caspofungin trough concentrations by 44%, requiring potential dose adjustment 5
• The small patient numbers in neonatal/infant studies (n=18 for <3 months, n=9 for 10-22 months) preclude definitive dosing recommendations, so close clinical monitoring is essential 1, 2

Practical Dosing Algorithm

1. Calculate BSA using the Mosteller formula or pediatric nomogram (for 6 kg infant ≈ 0.33 m²)
2. Day 1: Administer 70 mg/m² as loading dose (approximately 23 mg for this patient)
3. Day 2 onward: Administer 50 mg/m² once daily (approximately 16.5 mg for this patient)
4. Round to practical vial sizes based on available concentrations (typically supplied as 50 mg or 70 mg vials for reconstitution)
5. Infuse over 1 hour in compatible IV solution
6. Monitor clinical response and liver function every 2-3 days initially