Acyclovir Dosing Calculation for 11.5kg Pediatric Patient
For an 11.5kg child requiring 20mg/kg of acyclovir using 400mg/5ml syrup, administer 5.75ml per dose.
Dosing Calculation
The calculation is straightforward:
- Total dose needed: 11.5kg × 20mg/kg = 230mg per dose 1
- Volume calculation: Using 400mg/5ml concentration, this equals (230mg ÷ 400mg) × 5ml = 5.75ml per dose 1
Practical Administration Considerations
For practical home administration, this dose can be rounded to 6ml (approximately 2.6% increase), which falls within acceptable rounding parameters used in pediatric dosing 2. However, if precision is required, use an oral syringe marked to 0.25ml increments to deliver exactly 5.75ml 3.
Dosing Frequency Context
The frequency of administration depends on the indication 1:
- Herpes simplex treatment: Typically 5 times daily for immunocompetent patients 1, 4
- Varicella (chickenpox): 4 times daily (20mg/kg per dose, maximum 800mg per dose) 1
- Herpes zoster: 5 times daily in immunocompetent patients 1
Critical Safety Points
Weight-based dosing is essential in pediatric patients due to immature drug elimination pathways and pharmacokinetic differences 3, 5. The actual measured weight of 11.5kg should be used for all calculations 3.
Monitor for adequate hydration during acyclovir therapy, as the drug is excreted renally and crystalluria can occur, particularly with higher doses 1, 6, 7. Ensure the child maintains adequate fluid intake throughout treatment 1.
Bioavailability considerations: Oral acyclovir has 10-20% bioavailability that decreases with increasing doses, but this is already accounted for in the 20mg/kg dosing recommendation 1. The medication may be administered with or without food 1.
Common Pitfalls to Avoid
- Do not use adult dosing: Maximum single doses apply (800mg for varicella/zoster), but weight-based calculation takes precedence in pediatric patients 1
- Do not round excessively: While minor rounding is acceptable for practical administration, significant dose reductions could compromise efficacy 2, 5
- Ensure proper measuring device: Use an oral syringe rather than household spoons for accurate dosing 3