What is the recommended pediatric dosing of acyclovir (oral and intravenous) for a child with normal renal function, including dose per kilogram, frequency, duration, and maximum dose?

Pediatric Acyclovir Dosing

For children with normal renal function, acyclovir dosing depends on the indication, route of administration, and age/weight of the child, with intravenous doses ranging from 10-20 mg/kg every 8 hours and oral doses of 20 mg/kg (maximum 400-800 mg) given 3-5 times daily.

Intravenous Acyclovir Dosing

Neonatal HSV Infections

• Neonatal CNS or disseminated disease: 20 mg/kg IV every 8 hours for 21 days 1
• Neonatal skin, eye, or mouth disease: 20 mg/kg IV every 8 hours for 14 days 1
• Critical consideration: For neonatal CNS disease, repeat CSF HSV DNA PCR at days 19-21 of therapy; do not discontinue acyclovir until CSF PCR is negative 1

Pediatric HSV Infections (Beyond Neonatal Period)

• CNS or disseminated disease: 10 mg/kg IV every 8 hours for 21 days 1
  • Some experts use body surface area dosing: 500 mg/m² IV every 8 hours for children >1 year 1
• Moderate to severe gingivostomatitis: 5-10 mg/kg IV every 8 hours until lesions regress, then switch to oral 1

Varicella-Zoster Virus (Severe/Immunocompromised)

• Severe chickenpox or zoster in immunocompromised children: 10 mg/kg IV every 8 hours for 7-10 days 1

Dosing Adjustments Based on Renal Function

Important caveat: Acyclovir is primarily renally excreted, and dose adjustment is critical to prevent nephrotoxicity 1, 2

• Children with augmented renal clearance (eGFR >250 mL/min/1.73 m²) may require higher doses: 15-20 mg/kg every 6 hours 3
• Standard dosing (10 mg/kg every 8 hours) is appropriate for normal eGFR (≤250 mL/min/1.73 m²) 3
• Nephrotoxicity risk: Doses >15 mg/kg or >500 mg/m² per dose are associated with increased renal dysfunction, particularly in older children and when combined with ceftriaxone 4

Oral Acyclovir Dosing

HSV Infections

• Mild gingivostomatitis: 20 mg/kg (maximum 400 mg) per dose orally 3 times daily for 5-10 days 1
• Genital herpes (children <45 kg): 20 mg/kg (maximum 400 mg) per dose orally 3 times daily for 5-14 days 1

Varicella (Chickenpox) in Immunocompetent Children

• Dose: 20 mg/kg (maximum 800 mg) per dose orally 4 times daily for 7-10 days or until no new lesions for 48 hours 1
• Alternative dosing studied: 10-20 mg/kg 4 times daily for 5-7 days 5, 6
• Treatment should begin within 24 hours of rash onset for maximum benefit 5

Herpes Zoster (Shingles)

• Dose: 20 mg/kg (maximum 800 mg) per dose orally 4 times daily for 7-10 days 1

Maximum Doses and Frequency

Key Dosing Parameters

• Maximum single oral dose: 800 mg 1, 5
• Maximum single IV dose: Generally corresponds to adult dosing when weight-based calculations exceed adult doses 2
• Frequency:
  • IV: Every 8 hours is standard; every 6 hours for higher doses in augmented renal clearance 3
  • Oral: 3-5 times daily depending on indication 1, 5

Duration of Therapy

• Neonatal HSV (CNS/disseminated): 21 days 1
• Neonatal HSV (skin/eye/mouth): 14 days 1
• Pediatric HSV encephalitis: 14-21 days minimum; children 3 months-12 years should receive minimum 21 days due to higher relapse rates (up to 29%) 1
• Mucocutaneous HSV: 5-14 days 1
• Varicella/zoster: 7-10 days 1

Special Populations and Considerations

Preterm and Term Neonates

• Term infants 0-8 months: 3 mg/kg per dose orally twice daily 1
• Infants 9-11 months: 3.5 mg/kg per dose orally twice daily 1
• Preterm infants (IV dosing by postmenstrual age):
  • <38 weeks PMA: 1.0 mg/kg per dose twice daily 1
  • 38-40 weeks PMA: 1.5 mg/kg per dose twice daily 1

  • 40 weeks PMA: 3.0 mg/kg per dose twice daily 1

• Preterm infants have significantly reduced clearance and prolonged half-life (10-15 hours vs. 2.5 hours in older children) 7, 8

Bioavailability and Administration

• Oral bioavailability: 10-20%, decreasing with higher doses 5, 7
• Acyclovir may be administered with or without food 5
• Oral suspension concentration: 6 mg/mL when reconstituted 1

Monitoring and Toxicity Prevention

• Renal function monitoring is essential: Most renal dysfunction occurs within 48 hours of initiation 4
• Hydration: Maintain adequate hydration to reduce crystalluria risk 1
• Nephrotoxicity risk factors: Age >8 years, doses >15 mg/kg or >500 mg/m², concomitant ceftriaxone 4
• Neurotoxicity: More common in elderly but can occur in children with renal impairment; symptoms include confusion, hallucinations, altered consciousness 9
• Monitor for neutropenia, particularly with prolonged therapy 1

Common Pitfalls

• Failure to adjust for renal function: Both impaired and augmented renal clearance require dose modifications 3, 4
• Inadequate treatment duration for CNS disease: Stopping at 14 days instead of 21 days increases relapse risk, especially in young children 1
• Not confirming CSF clearance in neonatal CNS disease: Always repeat CSF PCR before discontinuing therapy 1
• Dosing above nephrotoxicity thresholds: Keep doses ≤500 mg/m² or ≤15 mg/kg outside neonatal period to minimize renal injury 4