What is the recommended first‑line therapy for a 9‑year‑old child with an oral herpes simplex virus type 1 lesion on the lip?

Treatment of HSV-1 Lip Lesion in a 9-Year-Old Child

For a 9-year-old child with an oral HSV-1 lesion on the lip, initiate oral acyclovir 20 mg/kg per dose (maximum 400 mg) three times daily for 5–10 days, continuing until all lesions are completely healed. 1, 2

First-Line Oral Antiviral Therapy

Oral acyclovir is the recommended first-line treatment for pediatric HSV-1 lip lesions (herpes labialis). 1, 2 The CDC-recommended dosing is:

• Acyclovir 20 mg/kg per dose (maximum 400 mg per dose)
• Administered three times daily
• Duration: 5–10 days, continuing until complete lesion healing 1, 2

Practical Dosing Example

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

• Calculated dose: 30 kg × 20 mg/kg = 600 mg, capped at 400 mg per dose
• Using acyclovir oral suspension (200 mg/5 mL): administer 10 mL three times daily 2

Critical Timing Considerations

Treatment must be initiated as early as possible—ideally during the prodromal phase (tingling, burning) or within the first 24 hours of lesion appearance—because peak HSV-1 viral titers occur in the first 24 hours. 1, 2 Starting treatment after this window markedly reduces clinical efficacy and prolongs lesion duration. 1

Treatment Duration and Endpoint

Do not stop acyclovir when symptoms improve; continue therapy until all lesions are fully crusted and healed. 1, 2 Stopping early may lead to suboptimal outcomes and prolonged viral shedding. 2 The typical course is 5–10 days, but the clinical endpoint—complete healing—takes priority over a fixed duration. 1, 2

Alternative Oral Antiviral Options

While acyclovir is the standard pediatric choice, valacyclovir and famciclovir are effective alternatives in adolescents ≥12 years but have less robust pediatric dosing data for younger children. 1, 3

For adolescents (postpubertal children):

• Valacyclovir 2 g twice daily for 1 day (single-day high-dose regimen) 1
• Famciclovir 1500 mg as a single dose 1

These short-course regimens offer superior convenience and adherence compared to multi-day acyclovir schedules in older children. 1

When to Escalate Care

Hospitalization and intravenous acyclovir (5–10 mg/kg every 8 hours) are indicated if:

• The child cannot maintain adequate oral intake due to severe oral pain or extensive lesions 1, 2
• Signs of disseminated disease, encephalitis, or immunocompromise are present 2
• The child fails to respond after 5–7 days of appropriate oral therapy (consider acyclovir-resistant HSV) 1, 2

For confirmed acyclovir-resistant HSV (rare in immunocompetent children), switch to intravenous foscarnet 40 mg/kg every 8 hours. 1, 2

Safety and Monitoring

Ensure adequate hydration throughout treatment to prevent acyclovir crystalluria and renal toxicity. 2 Monitor for clinical improvement within 48–72 hours. 2 Dose adjustment is required if renal insufficiency develops, as acyclovir is eliminated primarily by the kidneys. 2

The most common adverse effect in children is neutropenia (21–46% with prolonged therapy), though typically self-limited. 2 Headache, nausea, and diarrhea occur in fewer than 10% of patients and are usually mild. 1

Common Pitfalls to Avoid

• Do not rely on topical antivirals alone—they provide only modest benefit and are substantially less effective than oral therapy because they cannot reach the site of viral reactivation. 1, 2
• Do not discontinue treatment at a fixed 7-day interval if lesions have not fully crusted; continue until complete healing. 1, 2
• Do not delay treatment initiation—efficacy decreases significantly when started after the first 24 hours. 1, 2

Preventive Counseling

Advise the child and family to:

• Apply sunscreen (SPF ≥15) or zinc oxide to the lips before sun exposure to prevent UV-triggered recurrences 1, 4
• Identify and avoid personal triggers (fever, stress, sun exposure) 1
• Avoid direct contact (kissing, sharing utensils) until all lesions are fully crusted, as the child remains contagious throughout this period 1

Suppressive Therapy for Frequent Recurrences

If the child experiences six or more recurrences per year, consider daily suppressive therapy with acyclovir 400 mg twice daily, which reduces recurrence frequency by ≥75%. 1 Safety and efficacy have been documented for acyclovir for up to 6 years of continuous use. 1 After 1 year of suppression, reassess recurrence frequency, as it often decreases over time. 1