What is the appropriate pediatric dosage of acyclovir?

Pediatric Acyclovir Dosing

Acyclovir dosing in children is indication-specific and weight-based, ranging from 10-20 mg/kg per dose depending on the severity and type of herpes virus infection being treated.

Intravenous (IV) Dosing

Severe/CNS Infections

• CNS or disseminated HSV disease (non-neonatal): 10 mg/kg IV every 8 hours for 21 days 1
• Neonatal HSV encephalitis or disseminated disease: 20 mg/kg IV every 8 hours for 21 days 1
  • Higher dose (20 mg/kg) in neonates has decreased mortality to 5% with better developmental outcomes 2
  • Confirm CSF HSV DNA PCR is negative at days 19-21 before stopping therapy 1
• Neonatal skin/eye/mouth disease: 20 mg/kg IV every 8 hours for 14 days 1

Moderate Infections

• Moderate to severe gingivostomatitis: 5-10 mg/kg IV every 8 hours, then transition to oral when lesions regress 1

Special Considerations for IV Dosing

• Some experts use body surface area dosing (500 mg/m² every 8 hours) in children >1 year instead of weight-based dosing 1
• Children with augmented renal clearance (eGFR >250 ml/min/1.73 m²): May require 15-20 mg/kg every 6 hours to achieve therapeutic levels 3
• Standard renal function (eGFR ≤250 ml/min/1.73 m²): 10 mg/kg every 6 hours is appropriate 3

Oral Dosing

Mucocutaneous HSV Infections

• Mild gingivostomatitis: 20 mg/kg (max 400 mg/dose) orally 3 times daily for 5-10 days 1
• Genital herpes in children <45 kg: 20 mg/kg (max 400 mg/dose) orally 3 times daily for 5-14 days 1
• Genital herpes in adolescents/adults: 400 mg orally twice daily for 5-14 days 1

Chickenpox (Varicella)

• Children ≥2 years and <40 kg: 20 mg/kg (max 800 mg/dose) orally 4 times daily for 5 days 4
• Children >40 kg and adults: 800 mg orally 4 times daily for 5 days 4
• Initiate within 24 hours of rash onset for maximum efficacy 4

Herpes Zoster

• Standard dose: 800 mg orally 5 times daily for 7-10 days 4

Dosing Adjustments

Renal Impairment

Dose reduction is mandatory based on creatinine clearance 4:

• CrCl >10 mL/min: Standard dosing intervals
• CrCl 0-10 mL/min:
  • 200 mg dose: every 12 hours
  • 400 mg dose: 200 mg every 12 hours
  • 800 mg dose: 800 mg every 12 hours
• Hemodialysis: Administer additional dose after each dialysis session 4

Age-Specific Considerations

• Neonates (<1 month): Elimination half-life is 10-15 hours (vs 2.5 hours in older children), requiring careful monitoring 5
• Infants 1-3 months: May need dose adjustment to 24 mg/kg 3 times daily due to immature renal function 5
• Bioavailability is approximately 10-20% for oral formulations and decreases with increasing doses 4

Safety Monitoring

Neutropenia Risk

• Monitor ANC at least twice weekly during high-dose IV therapy 2
• 21% of patients receiving 60 mg/kg/day may develop neutropenia, typically with ANC 500-1000/mm³ 2
• Usually resolves without dose adjustment or after therapy completion 2

Nephrotoxicity

• Supra-therapeutic dosing significantly increases AKI risk (adjusted OR 12.9) 6
• No significant difference in renal injury between standard-dose (30 mg/kg/day) and high-dose (60 mg/kg/day) when dosed appropriately 7
• Ensure adequate hydration during IV administration 4

Key Clinical Pearls

Weight-based dosing is critical: Use actual body weight for non-obese patients and adjusted body weight for obese patients to optimize outcomes while minimizing toxicity 6

Duration matters: The 21-day course for CNS disease is essential—shorter courses (10 days) have inferior outcomes 2

Early initiation is paramount: For encephalitis, delays >2 days from hospital admission to acyclovir initiation predict poor outcomes 8

Therapeutic drug monitoring: Consider in children with augmented renal clearance or those not responding to standard dosing 3