What is the recommended dose of valacyclovir (Valtrex) for treating varicella in pediatric and adult patients with normal and impaired renal function?

Valacyclovir Dosing for Varicella

For varicella treatment in children aged 2 to <18 years with normal renal function, valacyclovir is dosed at 20 mg/kg three times daily for 5 days (maximum 1 gram per dose), while adults receive 1 gram three times daily for 7 days. 1

Pediatric Dosing (Ages 2 to <18 Years)

Standard Dosing for Normal Renal Function

• 20 mg/kg administered three times daily for 5 days 1
• Maximum single dose: 1 gram 1
• Therapy should be initiated at the earliest sign or symptom of varicella 1

Age-Specific Considerations

• Valacyclovir is FDA-approved for chickenpox treatment in immunocompetent children aged 2 to <18 years 1
• For children under 2 years, no FDA-approved valacyclovir dosing exists 1
• Infants 1-3 months show approximately 60% higher drug exposure than older children at the same mg/kg dose, making dosing recommendations unreliable in this age group 2

Extemporaneous Oral Suspension Preparation

• When tablets cannot be swallowed, a 25 mg/mL or 50 mg/mL suspension can be compounded from 500 mg tablets using Suspension Structured Vehicle USP-NF 1
• The prepared suspension must be refrigerated at 2-8°C and discarded after 28 days 1
• Shake well before each use 1

Adult Dosing (≥18 Years)

Herpes Zoster (Not Chickenpox, But Relevant for VZV)

• 1 gram orally every 8 hours for 7 days 1
• Most effective when started within 48 hours of rash onset 1

Renal Dose Adjustments

Pediatric Patients with Renal Impairment

• No data available for children with creatinine clearance <50 mL/min/1.73 m² 1
• Use acyclovir instead in this population, as dosing guidance exists 3, 4

Adult Patients with Renal Impairment (Herpes Zoster Dosing)

• CrCl 30-49 mL/min: 1 gram every 12 hours 1
• CrCl 10-29 mL/min: 1 gram every 24 hours 1
• CrCl <10 mL/min: 500 mg every 24 hours 1
• Hemodialysis patients: Administer dose after dialysis session 1
• Peritoneal dialysis: No supplemental dosing required beyond adjustments for CrCl <10 mL/min 1

Clinical Context and Alternative Considerations

When Valacyclovir May Not Be Appropriate

• Immunocompromised children should receive IV acyclovir (10 mg/kg every 8 hours) rather than oral valacyclovir for severe varicella 3
• HIV-infected children with moderate immunosuppression can use oral acyclovir 20 mg/kg four times daily (maximum 800 mg/dose) for 7-10 days 3, 4
• Healthy children with uncomplicated varicella may not require antiviral therapy at all, as supportive care is often sufficient 5

Acyclovir as the Standard Alternative

• Oral acyclovir remains the more established option for pediatric varicella: 20 mg/kg four times daily (maximum 800 mg/dose) for 7-10 days 3, 4
• Acyclovir has more extensive pediatric safety data and dosing guidance across all age groups and renal function levels 3
• For infants under 2 years, acyclovir is preferred due to lack of valacyclovir data 1, 2

Pharmacokinetic Advantages of Valacyclovir

• Valacyclovir provides 3-5 times better oral bioavailability than acyclovir, allowing less frequent dosing (three times daily vs. four times daily) 2, 6
• The 20 mg/kg three-times-daily valacyclovir dose produces acyclovir blood concentrations comparable to standard acyclovir dosing 2, 7
• Dose proportionality exists across the 10-20 mg/kg range in children aged 3 months to 11 years 2

Critical Safety Considerations

Monitoring Requirements

• Watch for bacterial superinfection (most common complication requiring hospitalization), particularly invasive group A streptococcal infections manifesting as expanding erythema, purulent drainage, increasing pain, or systemic toxicity 5
• Monitor for dehydration, pneumonia, and encephalitis as additional serious complications 5

Contraindications and Precautions

• Adjust dosing in renal impairment to prevent acyclovir accumulation and potential neurotoxicity 1
• Ensure adequate hydration during therapy 1
• No specific drug interactions require dose adjustment, but monitor renal function if used with other nephrotoxic agents 1

Common Pitfalls to Avoid

• Do not use valacyclovir in children under 2 years due to lack of FDA approval and safety data 1
• Do not assume adult dosing applies to adolescents - use weight-based dosing (20 mg/kg TID, max 1 gram) until age 18 1
• Do not delay treatment - efficacy is highest when started at earliest symptom onset 1
• Do not use valacyclovir for immunocompromised patients with severe disease - IV acyclovir is required 3
• Do not forget renal dose adjustments in adults - failure to adjust can lead to neurotoxicity 1