Acyclovir Dosing for Chickenpox Treatment
For otherwise healthy children with chickenpox, administer oral acyclovir 20 mg/kg (maximum 800 mg per dose) four times daily for 5 days, initiated within 24 hours of rash onset. 1, 2
Dosing by Patient Population
Healthy Children (2-12 years)
- 20 mg/kg orally four times daily for 5 days (maximum 800 mg per dose) 1, 2, 3
- Must be initiated within 24 hours of rash onset for optimal benefit 1, 4, 3
- Five days of therapy is equivalent to 7 days—no additional benefit from longer courses 4
Adolescents and Adults (≥12 years)
- 800 mg orally four times daily (or five times daily) for 5-7 days 1, 2, 5
- Treatment within 24 hours of rash onset provides the greatest clinical benefit 4, 5
- Adults with mild disease enrolled after 24 hours show only partial benefits 5
Immunocompromised Patients
- Intravenous acyclovir 10 mg/kg every 8 hours (or 500 mg/m²) 6, 7
- Duration: 7-10 days for moderate to severe disease, potentially longer depending on clinical response 6
- For CNS involvement: 21 days of IV therapy required 6
- Adequate hydration and monitoring of renal function and mental status are essential at these doses 7
Critical Timing Considerations
The 24-hour window from rash onset is the most important determinant of treatment efficacy. 1, 4, 3
- Patients treated on day 1 of rash experience significantly shortened illness duration, fewer lesions, and faster healing 4, 3
- Treatment initiated on day 2 (24-48 hours after rash) shows some benefit but is less dramatic 4, 5
- Treatment after 48 hours provides minimal clinical benefit in immunocompetent patients 4, 5
Expected Clinical Benefits
When initiated within 24 hours, acyclovir treatment results in:
- Fewer total lesions (median 294 vs 347 with placebo) 3
- Cessation of new lesion formation by day 3 in >95% of patients 3
- Reduced duration of fever to 3-4 days (vs >4 days in 20% of placebo recipients) 3
- Decreased itching and need for antipruritic therapy 5
- Faster progression to crusted and healed stages 3, 8
Important Caveats and Limitations
Acyclovir does not reduce transmission of varicella or decrease school absence duration. 1
- The drug does not eradicate latent virus or affect subsequent risk of herpes zoster 6
- Studies could not demonstrate statistically significant reduction in complications (1-2% incidence) due to their rarity 1
- Antibody titers after infection are not substantially different between treated and untreated patients 1, 3
- Viral resistance does not develop during short-term treatment courses 4
Special Population Considerations
Pregnant Women
- Acyclovir is FDA Category B 1
- Routine use is not recommended for uncomplicated varicella 1
- Intravenous acyclovir should be considered for serious complications such as pneumonia 1
High-Risk Groups Who Should Receive Treatment
The American Academy of Pediatrics recommends considering acyclovir for: 1
- Persons aged >12 years
- Those with chronic cutaneous or pulmonary disorders
- Patients on long-term salicylate therapy
- Those receiving short, intermittent, or aerosolized corticosteroids
- Secondary household contacts (some experts recommend) 1
Safety Profile
Acyclovir is well-tolerated in immunocompetent patients. 2, 3