What is the recommended dose of acyclovir (antiviral medication) for pediatric patients with herpes simplex virus (HSV) infections?

Pediatric Acyclovir Dosing for HSV Infections

For most pediatric HSV infections, use oral acyclovir 20 mg/kg per dose (maximum 400 mg/dose) three times daily for 5-10 days, and for severe disease requiring hospitalization, start with IV acyclovir 5-10 mg/kg per dose three times daily, then transition to oral dosing once lesions begin to regress. 1

Dosing by Clinical Presentation

Mild to Moderate Mucocutaneous HSV Disease

This includes herpetic gingivostomatitis, eczema herpeticum, genital herpes, and herpetic whitlow:

• Oral acyclovir: 20 mg/kg per dose (maximum 400 mg/dose) three times daily for 5-10 days 1, 2, 3
• This applies to children <45 kg 1
• Continue therapy until lesions completely heal, not just until improvement begins 3
• Expect clinical improvement within 48-72 hours of starting treatment 2, 3

Moderate to Severe Symptomatic Gingivostomatitis or Eczema Herpeticum

When hospitalization is required:

• Start with IV acyclovir: 5-10 mg/kg per dose three times daily 1, 2
• After lesions begin to regress, switch to oral acyclovir at the same weight-based dosing (20 mg/kg/dose three times daily) 1, 2
• Continue until complete healing occurs 1

CNS or Disseminated HSV Disease (Outside Neonatal Period)

For encephalitis or disseminated infection:

• IV acyclovir: 10 mg/kg per dose three times daily for 21 days 1, 3
• Alternative dosing for children >1 year: 500 mg/m²/dose IV every 8 hours 1, 3
• For neonatal CNS disease, repeat CSF HSV DNA PCR at days 19-21 and do not stop acyclovir until CSF PCR is negative 1

Neonatal HSV Infections (Special Population)

Neonates require substantially higher doses:

• IV acyclovir: 20 mg/kg every 8 hours 3
• Duration: 14 days for skin, eye, or mouth disease; 21 days for CNS or disseminated disease 3

Critical Safety Considerations

Hydration and Renal Monitoring

• Ensure adequate hydration throughout treatment to prevent crystalluria and renal toxicity 2, 3
• Monitor serum creatinine, especially in neonates and those on prolonged therapy 4, 5
• Dose adjustment required if renal insufficiency develops 3
• Renal injury occurs in approximately 3-10% of children on high-dose therapy, though usually not severe 4, 5

Hematologic Monitoring

• Neutropenia occurs in 21-46% of infants on prolonged therapy, though typically self-limited 3
• This is the most common adverse effect in young children 3

Treatment Timing and Duration

• Initiate treatment within the first 3 days of symptom onset for maximum efficacy, as peak viral replication occurs in the first 24 hours after lesion onset 3
• Do not stop treatment early when symptoms improve; continue until complete healing 1, 3

Acyclovir-Resistant HSV

If the child fails to respond after 5-7 days of appropriate acyclovir therapy:

• Switch to IV foscarnet: 40 mg/kg per dose three times daily (or 60 mg/kg per dose twice daily) 1, 3

Common Pitfalls to Avoid

• Do not use topical antivirals alone - they cannot reach the site of viral reactivation or impact the host immune response 3
• Do not stop treatment when lesions improve - continue until complete healing occurs 1, 3
• Do not underdose in children with augmented renal clearance - some may require higher or more frequent dosing 6

Alternative Agents for Older Children

For postpubertal children who can swallow tablets:

• Valacyclovir: 1 gram orally twice daily (no pediatric preparation exists for younger children) 1
• Famciclovir: 500 mg orally twice daily (limited pediatric data) 1