Maximum Dose of Acyclovir in Pediatrics
The maximum dose of acyclovir in pediatric patients is 800 mg per dose for oral administration, regardless of the calculated weight-based dose, and dosing should not exceed this cap even in larger children. 1
Oral Acyclovir Maximum Dosing
For oral acyclovir, the absolute maximum is 800 mg per dose, which applies across all pediatric indications including chickenpox and herpes zoster. 1, 2
Weight-Based Dosing with Maximum Cap:
- Standard oral dose: 20 mg/kg per dose, maximum 800 mg/dose 1, 2
- Frequency: 4 times daily for most indications (chickenpox, zoster) 1, 2
- Duration: 7-10 days or until no new lesions for 48 hours 1, 2
This means a 50 kg child would calculate to 1,000 mg per dose (20 mg/kg × 50 kg), but the dose must be capped at 800 mg. 1
Intravenous Acyclovir Maximum Dosing
For IV acyclovir, the dosing approach differs and maximum doses are not explicitly capped in the same way as oral formulations, but are based on either weight or body surface area:
Weight-Based IV Dosing:
- Standard IV dose: 10 mg/kg per dose, every 8 hours 1, 2
- High-dose IV regimen: 20 mg/kg per dose, every 8 hours (used for severe infections, neonatal HSV, or augmented renal clearance) 3, 4
- Neonatal HSV high-dose: 60 mg/kg/day divided into doses (20 mg/kg every 8 hours) 4
Body Surface Area-Based IV Dosing:
- Alternative dosing method: 500 mg/m² per dose, every 8 hours for children >1 year 1
- This method is preferred by some experts as it may provide more consistent drug exposure across different body sizes 1
Clinical Context for Maximum Dosing
The 800 mg oral maximum is derived from adult dosing studies and FDA approval, where 800 mg represents the standard adult dose for conditions like herpes zoster. 5 The CDC guidelines explicitly state this maximum to prevent excessive dosing in larger pediatric patients who might otherwise receive supraphysiologic doses. 1
Important Caveats:
Renal function adjustment is mandatory - all maximum doses assume normal renal function and must be reduced in patients with impaired creatinine clearance. 5, 6
Augmented renal clearance in critically ill children may require higher IV doses (15-20 mg/kg every 6 hours) to achieve therapeutic concentrations, but this applies only to IV formulations. 3
Age-specific considerations: Neonates have dramatically prolonged half-lives (10-15 hours in first month vs. 2.5 hours after 1 month), requiring less frequent dosing intervals despite similar mg/kg doses. 7
Safety Profile at Maximum Doses
High-dose acyclovir (60 mg/kg/day IV) has been studied in neonates and found to have acceptable safety, with thrombocytopenia (25% of infants) being more common than renal toxicity (2% with elevated creatinine, 0% requiring dialysis). 4 In older children, standard versus high-dose acyclovir showed similar rates of renal injury (3.1% vs 10.3%, p=0.34). 6
Hydration is critical - adequate fluid administration reduces nephrotoxicity risk at all dose levels. 8, 5