What is the recommended dosage of acyclovir (antiviral medication) for children with varicella (chickenpox)?

Acyclovir Dosage for Children with Varicella

For children with chickenpox, the recommended oral acyclovir dose is 20 mg/kg (maximum 800 mg) four times daily for 5 days, initiated within 24 hours of rash onset. 1

Standard Treatment Dosing

• Children 2 years and older: 20 mg/kg per dose orally 4 times daily (total 80 mg/kg/day) for 5 days 1
• Children over 40 kg: 800 mg orally 4 times daily for 5 days (adult dose) 1
• Timing is critical: Treatment should be initiated within 24 hours of rash onset for maximum efficacy 1, 2

Immunocompromised Children

For HIV-infected or immunocompromised children with varicella, the dosing differs based on disease severity:

• Mild disease (no or moderate immunosuppression): 20 mg/kg orally (maximum 800 mg/dose) 4 times daily for 7-10 days or until no new lesions for 48 hours 3
• Severe immunosuppression: 10 mg/kg IV every 8 hours for 7-10 days, followed by oral therapy 3
• Some experts recommend dosing based on body surface area (500 mg/m²/dose IV every 8 hours) for children over 1 year 3

Clinical Efficacy and Considerations

When started within 24 hours of rash, acyclovir treatment provides:

• Fewer total lesions (294 vs 347 in placebo) 2
• Cessation of new lesion formation by day 3 in over 95% of patients 2
• Reduced duration of fever and constitutional symptoms to 3-4 days 2
• Less itching and faster progression to crusted/healed stages 2

Important caveat: The American Academy of Pediatrics does not recommend routine acyclovir for all healthy children with chickenpox, as the clinical benefit may not justify routine use 3. However, acyclovir should be considered for:

• Children ≥12 years of age 3, 4
• Those with chronic cutaneous or pulmonary disorders 3, 4
• Children receiving long-term salicylate therapy 3
• Secondary household cases (per some experts) 3

Renal Dosing Adjustments

For children with renal impairment, dose modifications are necessary 1:

• Creatinine clearance 10-25 mL/min/1.73m²: 800 mg every 8 hours
• Creatinine clearance 0-10 mL/min/1.73m²: 800 mg every 12 hours
• Hemodialysis patients: Administer additional dose after each dialysis 1

Alternative Formulations

• Valacyclovir (acyclovir prodrug) can be used in children ≥2 years: 20 mg/kg three times daily for 5 days for varicella-zoster infections 5
• Valacyclovir provides enhanced bioavailability compared to oral acyclovir 5
• No pediatric formulation of famciclovir is available 3

Safety Profile

• Acyclovir is well-tolerated in children 2
• Does not interfere with antibody development or immune response 3, 4
• Does not alter future herpes zoster risk 4
• Mild, self-limiting diarrhea may occur in some patients 6