What is the recommended dose of oral acyclovir (antiviral medication) for a 2-year-old child with mucocutaneous Herpes Simplex Virus (HSV) infection?

Oral Acyclovir Dosing for Mucocutaneous HSV in a 2-Year-Old Child

For a 2-year-old child with mucocutaneous HSV infection, administer oral acyclovir 20 mg/kg per dose (maximum 400 mg/dose) three times daily for 5-10 days, continuing treatment until lesions completely heal. 1, 2

Standard Dosing Regimen

• The CDC-recommended dose is 20 mg/kg body weight per dose, with a maximum single dose of 400 mg, given three times daily 1, 2, 3
• Treatment duration should be 5-10 days for mild to moderate mucocutaneous HSV infections including gingivostomatitis, eczema herpeticum, or herpetic whitlow 1, 2
• Continue therapy until lesions completely heal, not just until clinical improvement begins 2, 3

Practical Example for a 2-Year-Old

• For a typical 2-year-old weighing approximately 12 kg: 12 kg × 20 mg/kg = 240 mg per dose, three times daily 1
• This weight-based calculation remains well below the 400 mg maximum single dose cap 1

Monitoring and Expected Response

• Monitor for clinical improvement within 48-72 hours of initiating therapy 1, 2, 3
• Treatment is most effective when started within the first 3 days of symptom onset, ideally within 24 hours 2
• Ensure adequate hydration throughout treatment to prevent crystalluria 1, 2, 3

When to Escalate Therapy

• For moderate to severe disease requiring hospitalization, start with IV acyclovir 5-10 mg/kg per dose three times daily, then transition to oral therapy at the same weight-based dosing once lesions begin to regress 1, 2
• If the child fails to respond after 5-7 days of appropriate acyclovir therapy, consider acyclovir-resistant HSV and switch to IV foscarnet 40 mg/kg per dose three times daily 2, 3

Important Safety Considerations

• Watch for neutropenia with prolonged use, though this is uncommon with standard 5-10 day courses 1
• Dose reduction is required if renal insufficiency develops, as acyclovir clearance is directly related to eGFR 1, 4
• The pediatric experience with oral acyclovir in children under 2 years is more limited than in older children, but available data support its safety and efficacy 2

Critical Pitfalls to Avoid

• Do not stop treatment early when symptoms improve; continue until complete healing occurs 2, 3
• Do not use topical antivirals alone, as they cannot reach the site of viral reactivation or adequately impact the host immune response 2
• Remember that acyclovir does not eradicate latent virus or affect the risk of future recurrences 1