What is the recommended dose of Meropenem (generic name) for a 1-month-old infant weighing 2.6 kg?

Meropenem Dosing for a 1-Month-Old Infant Weighing 2.6 kg

For this 1-month-old infant weighing 2.6 kg, administer meropenem 20 mg every 12 hours (40 mg/kg/day divided every 12 hours), given as an intravenous infusion over 30 minutes. 1

Dosing Calculation and Rationale

• This infant falls into the category: 32 weeks or older gestational age (GA) with postnatal age (PNA) less than 2 weeks, which requires 20 mg/kg every 8 hours for complicated intra-abdominal infections 1
• However, if the infant is 32 weeks or older GA with PNA of 2 weeks or older, the dose increases to 30 mg/kg every 8 hours 1
• For this 2.6 kg infant:
  • If PNA <2 weeks: 20 mg/kg = 52 mg per dose every 8 hours
  • If PNA ≥2 weeks: 30 mg/kg = 78 mg per dose every 8 hours 1

Critical Age-Specific Considerations

• The FDA labeling specifically addresses infants less than 3 months of age, stratifying dosing by both gestational age and postnatal age, which is essential for proper dosing in this vulnerable population 1
• Infants less than 32 weeks GA with PNA less than 2 weeks receive 20 mg/kg every 12 hours (longer dosing interval due to immature renal function) 1
• Infants less than 32 weeks GA with PNA 2 weeks and older receive 20 mg/kg every 8 hours 1
• There is no clinical experience with meropenem in pediatric patients with renal impairment, so careful monitoring is essential if renal dysfunction is suspected 1

Administration Guidelines

• Administer as an intravenous infusion over 30 minutes for all infants less than 3 months of age 1
• Do not administer as a bolus injection in this age group, as the safety data for bolus dosing is limited even in older pediatric patients 1
• Reconstitute vials with Sterile Water for Injection: for a 500 mg vial, add 10 mL to achieve approximately 50 mg/mL concentration 1

Pharmacokinetic Considerations in Neonates

• Meropenem has an elimination half-life of approximately 1 hour in adults, but this may be prolonged in neonates due to immature renal function 2
• Up to 70% of meropenem is recovered unchanged in urine, making renal function the primary determinant of drug clearance 2
• The volume of distribution is approximately 21L in adults (predominantly extracellular), but neonates may have different distribution characteristics 2

Important Clinical Pitfalls

• Do not use adult or older pediatric dosing regimens for infants under 3 months, as they require specific age-stratified dosing 1
• Verify both gestational age and postnatal age before calculating the dose, as both parameters affect the dosing interval 1
• Freshly prepared solutions should be used, and reconstituted solutions should not be frozen 1
• Do not mix meropenem with other drugs in the same solution, as compatibility has not been established 1
• Unlike imipenem, meropenem does not require coadministration with cilastatin because it is stable against renal dehydropeptidase-I 3, 4

Monitoring Recommendations

• Monitor for therapeutic response and consider therapeutic drug monitoring in critically ill neonates, as inadequate levels can lead to treatment failure 5
• Assess renal function if available, though specific dosing adjustments for neonatal renal impairment are not established 1
• Meropenem appears to have a lower risk of seizures compared to imipenem, which is particularly relevant in the neonatal population 4, 6