Acyclovir IV Dosing for Herpes in an 11-Year-Old Child
For an 11-year-old child weighing 24 kg with herpes infection requiring intravenous acyclovir, the dose is 10 mg/kg every 8 hours (30 mg/kg/day total), which equals 240 mg per dose or 720 mg/day for this patient.
Dosing Algorithm Based on Type of Herpes Infection
The specific dose depends on the severity and location of the herpes infection:
For Mucocutaneous HSV (Skin, Mouth, Genital)
- Dose: 10 mg/kg IV every 8 hours for 7 days 1, 2
- For this 24 kg child: 240 mg every 8 hours
- This applies to moderate-to-severe gingivostomatitis or immunocompromised patients 1
For CNS Disease (Encephalitis) or Disseminated Disease
- Dose: 10 mg/kg IV every 8 hours for 21 days 1, 2
- For this 24 kg child: 240 mg every 8 hours
- Duration is critical—21 days for CNS involvement 1
For Varicella-Zoster (Chickenpox/Shingles) in Immunocompromised
- Dose: 20 mg/kg IV every 8 hours for 7 days 1, 2
- For this 24 kg child: 480 mg every 8 hours
- Maximum single dose: 800 mg 1
Critical Dosing Considerations
The FDA-approved maximum dose is 20 mg/kg every 8 hours, not to be exceeded for any patient 2. However, the specific indication determines whether 10 mg/kg or 20 mg/kg is appropriate.
Age-Specific Guidance
For children under 12 years of age:
- Mucocutaneous HSV: 10 mg/kg every 8 hours 2
- HSV encephalitis (ages 3 months-12 years): 20 mg/kg every 8 hours 2
- Varicella-zoster in immunocompromised: 20 mg/kg every 8 hours 2
Administration Details
- Infuse each dose over 1 hour at a constant rate 2
- Never give as rapid bolus or IM/subcutaneous injection 2
- Ensure adequate hydration to prevent nephrotoxicity 2
Safety Monitoring
Monitor twice weekly during therapy:
- Serum creatinine and renal function 2
- Absolute neutrophil count (ANC)—neutropenia can occur, particularly at higher doses 3
- If ANC drops below 500/mm³, consider dose reduction or G-CSF 3
Common Pitfalls to Avoid
Underdosing in encephalitis: Using 10 mg/kg instead of 20 mg/kg for CNS disease leads to worse outcomes 2
Inadequate duration: Stopping at 10 days for CNS disease instead of completing 21 days increases relapse risk 1
Rapid infusion: Bolus administration causes nephrotoxicity and must be avoided 2
Ignoring renal function: Failure to adjust for renal impairment leads to toxicity 2
Body weight confusion: Some experts use body surface area (500 mg/m²/dose every 8 hours) for children >1 year, but weight-based dosing is standard 1, 2
Practical Calculation for This Patient
For a 24 kg, 11-year-old child:
- Mucocutaneous HSV: 240 mg IV every 8 hours × 7 days
- HSV encephalitis: 240 mg IV every 8 hours × 21 days
- Varicella-zoster (if immunocompromised): 480 mg IV every 8 hours × 7 days
Each dose should be diluted to ≤7 mg/mL concentration and infused over 1 hour 2.