What is the first‑line therapy for a healthy 9‑year‑old child with HSV‑1 infection presenting as primary gingivostomatitis or recurrent labial herpes?

First-Line Treatment for HSV-1 in a 9-Year-Old Child

For a healthy 9-year-old with HSV-1 infection, oral acyclovir 20 mg/kg per dose (maximum 400 mg) three times daily for 5-10 days is the first-line treatment, whether presenting as primary gingivostomatitis or recurrent labial herpes. 1

Dosing Algorithm

Weight-Based Calculation

• Calculate the dose by multiplying the child's weight in kilograms by 20 mg/kg 1
• Cap the maximum single dose at 400 mg 1
• Administer three times daily (every 8 hours) 1

Practical Dosing Example

For a typical 9-year-old weighing 30 kg:

• Calculated dose: 30 kg × 20 mg/kg = 600 mg
• Actual dose: 400 mg (capped at maximum) 1
• Using acyclovir suspension (200 mg/5 mL): give 10 mL three times daily 1

Treatment Duration and Endpoint

• Continue therapy for 5-10 days until all lesions are completely healed, not just improved 1, 2
• Do not stop treatment early when symptoms improve—this is a critical pitfall that leads to suboptimal outcomes 1
• Monitor for clinical improvement within 48-72 hours of starting therapy 1, 2

Timing Is Critical

Treatment must be initiated within the first 3 days of symptom onset for maximum efficacy 1, because:

• Peak viral replication occurs in the first 24 hours after lesion onset 1, 2
• Delaying treatment beyond 72 hours significantly reduces therapeutic benefit 1
• Starting during the prodromal phase (tingling, burning) provides the best outcomes 1

Disease Severity-Based Management

Mild to Moderate Disease (Outpatient)

• Use oral acyclovir at the weight-based dose described above 1, 2
• Ensure adequate oral hydration throughout treatment to prevent crystalluria and renal toxicity 1, 2
• This applies to most cases of primary gingivostomatitis and all recurrent labial herpes 1

Severe Disease Requiring Hospitalization

• Initiate IV acyclovir 5-10 mg/kg per dose three times daily 1, 2
• Indications for hospitalization include: inability to maintain oral intake due to severe oral pain, extensive lesions preventing adequate hydration, or signs of dehydration 1
• Once lesions begin to regress and the child can tolerate oral fluids, switch to oral acyclovir at the same weight-based dosing to complete the course 1, 2

Safety Monitoring

• Maintain adequate hydration throughout the treatment course to prevent acyclovir crystalluria and renal toxicity 1, 2
• The most common adverse effect in children on prolonged therapy is neutropenia (21-46% of infants), though typically self-limited 1
• Dose adjustment is required if renal insufficiency develops, as acyclovir is primarily eliminated by the kidneys 1

Management of Treatment Failure

• If the child shows no clinical response after 5-7 days of appropriate acyclovir therapy, consider acyclovir-resistant HSV 1, 2
• For confirmed resistance, switch to IV foscarnet 40 mg/kg per dose three times daily 1, 2
• Resistance is rare (<0.5%) in immunocompetent children but should be considered if lesions worsen or fail to improve 1

Common Pitfalls to Avoid

• Do not use topical antivirals alone—they cannot reach the site of viral reactivation in the sensory ganglia and are substantially less effective than oral therapy 1, 2, 3
• Do not stop treatment when symptoms improve—continue until complete lesion healing occurs 1, 2
• Do not delay treatment—efficacy decreases significantly after the first 72 hours of symptom onset 1
• Do not underdose—use the full weight-based calculation up to the 400 mg maximum 1

Recurrent HSV-1 Considerations

• For children with frequent recurrences (≥6 episodes per year), daily suppressive therapy with oral acyclovir can be considered 1
• The same weight-based dosing principles apply to both primary and recurrent infections 1
• Counsel families to identify and avoid triggers including UV light exposure, fever, and stress 2, 4

Formulation Notes

• Acyclovir oral suspension is available as 200 mg/5 mL 1
• If suspension is unavailable, pharmacies can compound a suspension from tablets following manufacturer instructions 1
• Ensure parents understand the dosing schedule and have a measuring device for accurate administration 1