What is the recommended dose of penicillin for a neonate?

Penicillin Dosing for Neonates

For neonates, penicillin G should be dosed at 25,000-50,000 IU/kg every 12 hours, with specific dosing based on gestational age, postnatal age, and weight. 1, 2, 3

Recommended Penicillin G Dosing by Age and Weight

Preterm Neonates

• Gestational age ≤28 weeks and <1200g: 25,000 IU (15 mg)/kg every 12 hours 3
• Gestational age ≤34 weeks:
  • Postnatal age ≤7 days: 50,000 IU/kg/day divided every 12 hours
  • Postnatal age >7 days: Increase to more frequent dosing intervals

Term and Near-Term Neonates

• Gestational age ≥32 weeks:
  • Postnatal age <72 hours: 25,000 IU/kg every 12 hours 2
  • For group B streptococcal infections: 25,000 IU/kg every 12 hours is sufficient 2

Pharmacokinetic Considerations

The pharmacokinetics of penicillin G in neonates differs significantly from adults due to:

• Extended half-life: 3.6-4.6 hours in neonates vs. approximately 0.5-1 hour in adults 2, 3
• Reduced clearance: Particularly in preterm neonates
• Larger volume of distribution: 0.50 L/kg (median) 2

These differences justify the less frequent dosing intervals (every 12 hours) compared to older children and adults.

Clinical Applications

For Congenital Syphilis

• Aqueous crystalline penicillin G: 50,000 units/kg IV every 12 hours for the first 7 days of life, then every 8 hours thereafter for a total of 10 days 1, 4
• Alternative: Procaine penicillin G 50,000 units/kg IM as a single daily dose for 10 days 1, 4

For Bacterial Infections

• Sepsis/Bacteremia: 25,000-50,000 IU/kg every 12 hours depending on gestational age 3, 5
• Meningitis: Higher doses may be required (consult specialist)

Monitoring and Adjustments

• Renal function: Penicillin G clearance correlates with creatinine clearance 3
• Duration of therapy: Typically 7-10 days for most infections, 10-14 days for congenital syphilis 1, 4

Important Considerations

• Penicillin G concentrations remain above MIC90 for common neonatal pathogens (including Group B streptococci) throughout the dosing interval with the recommended regimens 2, 3
• Lower doses (25,000 IU/kg every 12 hours) are generally sufficient and safe for very low birth weight infants 3
• No proven alternatives exist for treating congenital syphilis in neonates with penicillin allergy; desensitization should be considered 1, 4

Pitfalls to Avoid

1. Underdosing: Failure to adjust dosing based on gestational and postnatal age
2. Overdosing: Not accounting for reduced clearance in premature neonates
3. Inappropriate intervals: Using adult dosing intervals (every 4-6 hours) in neonates
4. Inadequate duration: Particularly for congenital syphilis, which requires a full 10-day course

Remember that dosing recommendations may need to be adjusted based on the specific infection being treated and the clinical response of the neonate.