What is the appropriate acyclovir dosage for a 4‑year‑old child with herpes zoster (shingles)?

Acyclovir Dosing for Shingles in a 4-Year-Old Child

For a 4-year-old child with herpes zoster (shingles), administer oral acyclovir 20 mg/kg per dose (maximum 800 mg/dose) four times daily for 7-10 days or until no new lesions appear for 48 hours. 1

Standard Dosing Regimen

• The CDC-recommended dose is 20 mg/kg body weight (maximum 800 mg/dose) given four times daily for 7-10 days for children with mild to moderate disease and normal immune function 1
• Treatment should be initiated as early as possible, ideally within 72 hours of rash onset, for maximum benefit 1
• Continue therapy until no new lesions have appeared for 48 hours 1

Practical Dosing Example

For a typical 4-year-old weighing approximately 16-18 kg:

• Dose would be 320-360 mg four times daily (20 mg/kg × 16-18 kg)
• This is well below the maximum single dose of 800 mg 1
• Oral suspension formulation is preferred for this age group given ease of administration 2

When to Escalate to IV Therapy

• Intravenous acyclovir is indicated for children with severe immunosuppression 1
• IV dosing for immunocompromised children: 10 mg/kg every 8 hours (or alternatively 500 mg/m² every 8 hours for children older than 1 year) 1, 3
• Duration remains 7-10 days or until no new lesions for 48 hours 1

Special Circumstances Requiring Immediate Attention

Ocular Involvement

• Herpes zoster ophthalmicus requires prompt ophthalmology referral 1
• Look for lesions on the tip of the nose (Hutchinson's sign), which indicates nasociliary nerve involvement and high risk of ocular complications 1
• Potential complications include keratitis, uveitis, corneal scarring, and secondary glaucoma 1

Acute Retinal Necrosis

• Requires IV acyclovir 10 mg/kg three times daily for 10-14 days, followed by prolonged oral therapy 1
• This is a vision-threatening emergency requiring immediate ophthalmology consultation 1

Common Pitfalls to Avoid

• Do not use valacyclovir or famciclovir in young children – these are reserved for older children who can receive adult dosing and swallow tablets 1, 2
• Ensure adequate hydration throughout treatment to prevent crystalluria 3
• Do not underdose based on concern about toxicity – the 20 mg/kg four-times-daily regimen is well-established and safe 1, 2
• For immunocompromised patients, do not use oral therapy when IV is indicated, as this may lead to treatment failure 1

Monitoring and Follow-up

• Assess for new lesion formation daily during the first 48 hours 1
• Monitor for signs of bacterial superinfection of lesions 1
• Watch for neurological complications, particularly if the rash involves the face or scalp 1
• Ensure renal function is adequate, especially if considering dose adjustments 4