Valacyclovir Dosing for a 20kg Child with Chickenpox
For a 20kg child with chickenpox, administer valacyclovir 20 mg/kg three times daily for 5 days, which equals 400 mg (8 mL of 50 mg/mL suspension) three times daily. 1
FDA-Approved Pediatric Dosing
The FDA label for valacyclovir (Valtrex) specifically states that for chickenpox treatment in immunocompetent pediatric patients aged 2 to less than 18 years, the recommended dose is 20 mg/kg administered 3 times daily for 5 days, with a maximum single dose not exceeding 1 gram. 1
For your 20kg patient, this calculates to:
- 400 mg per dose, three times daily
- Total daily dose: 1,200 mg
- Duration: 5 days 1
Preparation and Administration
Since solid dosage forms may not be appropriate for younger children, valacyclovir oral suspension can be extemporaneously compounded from 500-mg tablets at concentrations of either 25 mg/mL or 50 mg/mL. 1
For practical administration:
- Using 50 mg/mL suspension: Give 8 mL three times daily
- Using 25 mg/mL suspension: Give 16 mL three times daily 1
The suspension should be stored refrigerated at 2-8°C and discarded after 28 days. 1
Timing of Initiation
Therapy should be initiated at the earliest sign or symptom of chickenpox for maximum efficacy. 1 The Centers for Disease Control and Prevention emphasizes that treatment is most effective when started early in the disease course. 2
Important Clinical Considerations
Acyclovir remains the preferred first-line agent for chickenpox in children according to CDC guidelines, which recommend acyclovir 20 mg/kg orally (maximum 800 mg/dose) 4 times daily for 7-10 days. 3, 2 However, valacyclovir offers the advantage of less frequent dosing (three times daily versus four times daily), which may improve adherence. 4
Pharmacokinetic studies demonstrate that valacyclovir 20 mg/kg three times daily in children aged 3 months through 11 years produces favorable acyclovir blood concentrations and is well tolerated. 4 The enhanced bioavailability of valacyclovir compared to acyclovir means fewer daily doses are needed to achieve therapeutic drug levels. 5
Critical Caveats
- Do not use in infants under 3 months of age due to decreased drug clearance in this population, which results in approximately 60% higher drug exposure. 4
- Valacyclovir does not eradicate latent virus or affect the risk of future recurrences. 2
- Ensure adequate hydration throughout the treatment course. 6
- The medication may be given without regard to meals. 1
Monitoring
Watch for clinical improvement within 48-72 hours of initiating therapy. 6 Monitor for neutropenia with prolonged use, though this is uncommon with standard 5-day courses. 6