What is the appropriate dose of acyclovir oral suspension (200 mg per 5 mL) for a 5‑year‑old child with an HSV‑1 oral lesion?

Acyclovir Dosing for HSV-1 Oral Lesions in a 5-Year-Old

For a 5-year-old child with HSV-1 oral lesions (gingivostomatitis), administer acyclovir oral suspension 20 mg/kg per dose (maximum 400 mg/dose) three times daily for 5-10 days, continuing until lesions completely heal. 1, 2, 3

Calculating the Specific Dose

• Weight-based calculation: Multiply the child's weight in kg by 20 mg/kg to determine the dose per administration 1
• Maximum dose cap: Do not exceed 400 mg per dose regardless of weight 1, 2
• Suspension concentration: With 200 mg/5 mL suspension, each 5 mL provides 200 mg
  • Example: For a 20 kg child: 20 kg × 20 mg/kg = 400 mg per dose = 10 mL three times daily 1
  • Example: For a 15 kg child: 15 kg × 20 mg/kg = 300 mg per dose = 7.5 mL three times daily 1

Treatment Duration and Monitoring

• Duration: Continue therapy for 5-10 days, but the critical endpoint is complete healing of all lesions, not just symptom improvement 1, 2, 3
• Timing is critical: 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 2, 3
• Expected response: Monitor for clinical improvement within 48-72 hours of starting therapy 2, 3

Severity-Based Treatment Algorithm

Mild to moderate gingivostomatitis (most common presentation):

• Oral acyclovir 20 mg/kg/dose (max 400 mg) three times daily 1, 2, 3
• Treat as outpatient with adequate hydration 2, 3

Moderate to severe gingivostomatitis requiring hospitalization:

• Start with IV acyclovir 5-10 mg/kg/dose three times daily 1
• After lesions begin to regress, transition to oral acyclovir at the same weight-based dosing to complete the course 1, 2

Critical Safety Considerations

• Hydration: Ensure adequate fluid intake throughout the treatment course to prevent acyclovir crystalluria 2, 3
• Neutropenia monitoring: Watch for neutropenia with prolonged use, though this is uncommon with standard 5-10 day courses and occurs more frequently in infants on extended therapy (21-46% in prolonged neonatal treatment) 2, 3
• Renal function: Dose adjustment is required if renal insufficiency develops during treatment 2

Common Pitfalls to Avoid

• Do not use topical acyclovir alone: Topical antivirals cannot reach the site of viral reactivation or impact the host immune response and are substantially less effective than oral therapy 4, 3
• Do not stop treatment early: Continue until complete healing occurs, not just when symptoms improve 1, 2, 3
• Do not delay treatment: Efficacy decreases significantly if treatment is not initiated within 72 hours of symptom onset 4, 2, 3

Treatment Failure Considerations

• If no response after 5-7 days: Consider acyclovir-resistant HSV and switch to IV foscarnet 40 mg/kg/dose three times daily 2, 3
• Resistance is rare in immunocompetent children but should be suspected with treatment failure 2, 3

Important Counseling Points

• Acyclovir does not eradicate latent virus or prevent future recurrences after discontinuation 4
• The medication treats the current outbreak but HSV-1 will remain dormant in nerve ganglia 4
• Adequate bioavailability is achieved with oral suspension (approximately 12% in young children), making oral therapy appropriate for mild to moderate disease 5