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Last Updated: 2/13/2026

Acyclovir Dosing Recommendations for Pediatric HSV and VZV Infections

HSV Central Nervous System and Disseminated Disease

  • For children (outside the neonatal period) with HSV encephalitis or disseminated disease, give acyclovir 10 mg/kg IV every 8 h for 21 days. 1 (CDC)
  • Perform a repeat CSF HSV DNA PCR at days 19‑21 of therapy and continue acyclovir until the PCR is negative. 1 (CDC)
  • British guidelines advise a minimum 21‑day course for children 3 months‑12 years because relapse rates can reach 26‑29 %. 2 (British Society for Infection)
  • Some experts use body‑surface‑area dosing (≈500 mg/m² IV every 8 h) for children > 1 year as an alternative to weight‑based dosing. 3 (CDC)

Neonatal HSV Infection (Birth – 3 months)

  • Skin/eye/mouth disease: acyclovir 20 mg/kg IV every 8 h for 14 days. 4 (CDC)
  • CNS disease: acyclovir 20 mg/kg IV every 8 h for 21 days. 4 (CDC)
  • A higher‑dose regimen (20 mg/kg IV every 8 h for 21 days) reduces mortality to ≈5 % and improves neurodevelopmental outcomes. 5 (Infectious Diseases Society of America)

Mucocutaneous HSV Infection

  • Moderate‑to‑severe gingivostomatitis: start IV acyclovir 5‑10 mg/kg every 8 h, then switch to oral formulation once lesions regress and continue until complete healing. 1 (CDC)
  • Mild gingivostomatitis or genital herpes (children < 45 kg): oral acyclovir 20 mg/kg (max 400 mg) three times daily for 5‑14 days. 1 (CDC)
  • Adolescents (≥ 45 kg): oral acyclovir 400 mg twice daily for 5‑14 days. 1 (CDC)

Varicella (Chickenpox) in Immunocompromised Children

  • Oral therapy: acyclovir 20 mg/kg (max 800 mg) four times daily for 7‑10 days or until no new lesions for 48 h. 6 (CDC)
  • Severe immunosuppression or complicated disease: IV acyclovir 10 mg/kg every 8 h. 3 (CDC)

Herpes Zoster (Shingles) in Children

  • Immunocompetent children: oral acyclovir 20 mg/kg (max 800 mg) four times daily for 7‑10 days, preferably started within 48‑72 h of rash onset. [6][3] (CDC)

VZV‑Related Retinal Infections

  • Acute retinal necrosis: IV acyclovir 10 mg/kg every 8 h for 10‑14 days, followed by oral valacyclovir 1 g three times daily (or oral acyclovir 20 mg/kg) for 4‑6 weeks. 6 (CDC)

Management of Acyclovir‑Resistant HSV/VZV

  • Use foscarnet 40 mg/kg IV every 8 h (or 60 mg/kg IV every 12 h) for resistant infections. 1 (CDC)

Safety Considerations

  • Up to 20 % of pediatric patients receiving IV acyclovir develop reversible nephropathy from crystalluria, typically after 4 days of therapy; maintain adequate hydration and monitor renal function. 2 (British Society for Infection)

CDC Recommendations for Antiviral Therapy in Pediatric HSV and VZV Infections

Herpes Simplex Virus (HSV) Management

  • Acyclovir is the preferred agent for mucocutaneous HSV (e.g., genital herpes, gingivostomatitis) in children weighing less than 45 kg, administered at 20 mg/kg orally three times daily (maximum 400 mg) for 5–14 days. This recommendation is based on CDC guidance and reflects the evidence‑based standard of care. 7

  • Valacyclovir lacks pediatric formulation and dosing data for HSV; it is approved only for adults/adolescents (1 g orally twice daily) and therefore should not be used in children. The CDC notes the limited pediatric data and advises against off‑label use. 7

  • Overall, valacyclovir has limited pediatric data for HSV infections, and acyclovir remains the evidence‑based choice for treatment in children. This overarching CDC statement supports the preference for acyclovir. [7][8]

Varicella‑Zoster Virus (VZV) Management

  • In immunocompetent children with herpes zoster, oral acyclovir should be given at 20 mg/kg (maximum 800 mg) four times daily for 7–10 days, initiated within 48–72 hours of rash onset. CDC recommends this regimen as the standard of care. 8

  • For immunocompromised children with severe immunosuppression or complicated herpes zoster, intravenous acyclovir is recommended at 10 mg/kg every 8 hours. This CDC guideline addresses the need for higher systemic exposure in high‑risk patients. 8

  • Immunocompromised children with mild‑to‑moderate immunosuppression may receive oral acyclovir at 20 mg/kg (maximum 800 mg) four times daily for 7–10 days. CDC provides this alternative oral regimen for less severe cases. 8

  • In cases of VZV‑associated acute retinal necrosis, CDC advises intravenous acyclovir 10 mg/kg every 8 hours for 10–14 days, followed by oral therapy (either valacyclovir 1 g three times daily or acyclovir 20 mg/kg) for 4–6 weeks in older children capable of adult dosing. This sequential approach is recommended to achieve adequate ocular viral suppression. 8

Management of Acyclovir‑Resistant HSV/VZV

  • Foscarnet is the treatment of choice for acyclovir‑resistant HSV or VZV infections in children. The CDC recommends this agent when resistance is confirmed. 7

  • Foscarnet dosing options include 40 mg/kg intravenously every 8 hours or 60 mg/kg intravenously every 12 hours, with infusion over 2 hours and appropriate fluid loading to mitigate renal toxicity. CDC provides these dosing regimens and administration precautions. 7

Acyclovir and Foscarnet Dosing for Pediatric HSV/VZV Infections

Neonatal Herpes Simplex Virus (HSV) Infections (Birth – 3 months)

  • Skin, eye, or mouth disease: Administer 20 mg/kg intravenously every 8 hours for 14 days in neonates. This regimen is recommended by the MMWR Recommendations and Reports. 9
  • Central nervous system or disseminated disease: Administer 20 mg/kg intravenously every 8 hours for 21 days in neonates. This higher‑dose protocol is endorsed by the MMWR Recommendations and Reports. 9

HSV CNS or Disseminated Disease Beyond the Neonatal Period (Children > 3 months)

  • Standard therapy: Give 10 mg/kg intravenously every 8 hours for 21 days in children older than three months with HSV encephalitis or disseminated disease. This dosing is supported by the MMWR Recommendations and Reports. 9

Mucocutaneous HSV (Gingivostomatitis, Genital Herpes)

  • Moderate‑to‑severe gingivostomatitis: Begin with 5–10 mg/kg intravenously every 8 hours, then transition to oral acyclovir once lesions start to regress and continue until complete healing. Recommended by the MMWR Recommendations and Reports. 9
  • Mild gingivostomatitis or genital herpes in children weighing < 45 kg: Use 20 mg/kg (maximum 400 mg) orally three times daily for 5–14 days. This regimen is outlined in the MMWR Recommendations and Reports. 9
  • Mild gingivostomatitis or genital herpes in adolescents weighing ≥ 45 kg: Use 400 mg orally twice daily for 5–14 days. This dosing is described in the MMWR Recommendations and Reports. 9

Management of Acyclovir‑Resistant HSV/VZV

  • First‑line alternative (Foscarnet): Administer 40 mg/kg intravenously every 8 hours or 60 mg/kg intravenously every 12 hours when resistance to acyclovir is confirmed. These dosing recommendations come from the MMWR Recommendations and Reports. 9

REFERENCES

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