What is the recommended dose of acyclovir (antiviral medication) for pediatric patients with herpes simplex labialis (cold sores)?

Pediatric Acyclovir Dosing for Cold Sores (Herpes Labialis)

For pediatric patients with cold sores, oral acyclovir 20 mg/kg per dose (maximum 400 mg/dose) three times daily for 5-10 days is the recommended treatment, initiated within the first 3 days of symptom onset. 1, 2

Standard Dosing Regimen

• Oral acyclovir: 20 mg/kg/dose (maximum 400 mg/dose) three times daily for 5-10 days 3, 1, 2
• Treatment must be started within the first 3 days of symptom onset for maximum efficacy, as peak viral replication occurs in the first 24 hours after lesion onset 1, 2
• Continue therapy until lesions completely heal, not just until clinical improvement is observed 3, 1, 2

Monitoring and Expected Response

• Monitor for clinical improvement within 48-72 hours of initiating therapy 3, 1, 2
• If no improvement occurs after 5-7 days of appropriate acyclovir therapy, consider acyclovir-resistant HSV and switch to intravenous foscarnet 40 mg/kg per dose three times daily 1, 2

Important Clinical Considerations

Timing is Critical

• The CDC emphasizes that early treatment within 3 days of symptom onset is essential for optimal efficacy 1, 2
• Delaying treatment beyond this window significantly reduces therapeutic benefit 1

Safety Profile

• Ensure adequate hydration throughout the treatment course to prevent crystalluria and renal toxicity 3, 1, 2
• Monitor for neutropenia with prolonged use (occurs in 21-46% of infants on extended therapy, though typically self-limited) 1
• Dose adjustment is required if renal insufficiency develops 1

Pediatric Experience

• 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 1
• The oral suspension formulation is well tolerated in young children 4

Common Pitfalls to Avoid

• Do not use topical antivirals alone - they cannot reach the site of viral reactivation or impact the host immune response 1, 2
• Do not stop treatment early when symptoms improve - continue until complete healing occurs to prevent recurrence 3, 1, 2
• Do not delay treatment - waiting beyond 3 days of symptom onset significantly reduces efficacy 1, 2

Alternative Considerations for Older Children

• For postpubertal children able to swallow adult-sized tablets, valacyclovir 500 mg twice daily may be considered, though this mirrors adult dosing and pediatric data are limited 5
• Valacyclovir provides enhanced acyclovir bioavailability but is not routinely recommended for younger children with simple cold sores 6