Oral Acyclovir Dosing for Chickenpox in a 24-kg Child
For a 24-kg boy with uncomplicated chickenpox, give oral acyclovir 480 mg (20 mg/kg) four times daily for 5 days, starting within 24 hours of rash onset for maximum benefit. 1, 2, 3
Dose Calculation and Administration
- Weight-based dosing: 20 mg/kg per dose, four times daily 1, 2, 3
- For this 24-kg child: 24 kg × 20 mg/kg = 480 mg per dose 1, 3
- Maximum single dose: 800 mg (not applicable here) 1, 2, 3
- Total daily dose: 1,920 mg/day (480 mg × 4 doses) 3
Practical Formulation Guidance
- Using oral suspension (6 mg/mL): Give 80 mL per dose (480 mg ÷ 6 mg/mL) 3
- Using capsules: Give one 75-mg capsule + four 100-mg capsules per dose, or compound to nearest available strength 3
- Administration: Can be given with or without food; giving with meals may improve tolerability 3
Treatment Duration and Timing
- Standard duration: 5 days is sufficient and equivalent to 7 days 4, 5
- Alternative duration: 7-10 days or until no new lesions for 48 hours (primarily for immunocompromised patients) 1, 2
- Critical timing: Must initiate within 24 hours of rash onset for optimal efficacy 4, 5
- Delayed treatment (24-48 hours): Still provides some benefit but significantly reduced compared to early initiation 5
Expected Clinical Benefits (When Started Early)
- Lesion reduction: Approximately 50 fewer lesions compared to placebo (294 vs 347 mean lesions) 4
- Accelerated healing: >95% of patients have no new lesions by day 3 (vs 20% still forming lesions on day 6+ with placebo) 4
- Symptom duration: Fever and constitutional symptoms limited to 3-4 days (vs >4 days in 20% of untreated patients) 4
- Reduced itching and faster progression to crusted/healed stages 4
Important Clinical Caveats
- Renal function: This dose assumes normal renal function; reduce dose if creatinine clearance is impaired 3, 6
- Immunocompromised patients: If this child has HIV or severe immunosuppression (not stated in question), consider IV acyclovir 10 mg/kg every 8 hours instead 1, 2
- Does not prevent complications: While acyclovir reduces symptom severity, it has not been proven to reduce rare serious complications like bacterial superinfection or cerebellar ataxia 4
- Does not affect immunity: Treatment does not interfere with varicella-zoster antibody development 3, 4
Common Pitfalls to Avoid
- Starting too late: Efficacy drops substantially if initiated >24 hours after rash onset; some benefit remains if started within 48 hours but significantly diminished 4, 5
- Underdosing: Do not use adult fixed-dose regimens (e.g., 800 mg) for children <40 kg; always calculate weight-based dosing 1, 3
- Inadequate hydration: Ensure adequate fluid intake to prevent acyclovir crystalluria, though this is more relevant with IV dosing 2, 6
- Topical formulations: Never use topical acyclovir for chickenpox—it is ineffective for systemic viral infections 7