Acyclovir Pediatric Dosing for Herpes Simplex Infections
For mild to moderate HSV infections in children, use oral acyclovir 20 mg/kg per dose (maximum 400 mg/dose) three times daily for 5-10 days, and for severe disease requiring hospitalization, use intravenous acyclovir 5-10 mg/kg per dose three times daily. 1
Standard Oral Dosing for Mild to Moderate Disease
The CDC recommends oral acyclovir 20 mg/kg per dose (maximum 400 mg/dose) three times daily for 5-10 days for common HSV infections including herpetic gingivostomatitis, eczema herpeticum, or herpetic whitlow 1, 2
Continue therapy until lesions completely heal, not just until clinical improvement begins 1
Monitor for clinical improvement within 48-72 hours of starting treatment 1, 2
Initiate treatment within the first 3 days of symptom onset for maximum efficacy, as peak viral replication occurs in the first 24 hours after lesion onset 1
Intravenous Dosing for Severe Disease
For severe HSV infections requiring hospitalization, start with intravenous acyclovir 5-10 mg/kg per dose three times daily 1, 2
After lesions begin to regress, transition to oral acyclovir at the same weight-based dosing (20 mg/kg per dose three times daily) to complete the treatment course 1
For disseminated HSV disease or encephalitis, use intravenous acyclovir 10 mg/kg/dose or 500 mg/m²/dose three times daily for 21 days 1
Special Population: Neonates
For neonates with HSV infections, use higher doses of intravenous acyclovir 20 mg/kg IV every 8 hours as recommended by the CDC 1, 2
Neonatal skin, eye, or mouth disease requires acyclovir 20 mg/kg IV three times daily for 14 days 1
The elimination half-life of acyclovir decreases sharply during the first month after birth, from 10-15 hours to 2.5 hours, justifying the higher dosing in neonates 3
Safety Monitoring and Adverse Effects
The most common adverse effect is neutropenia, occurring in approximately 21-46% of infants on prolonged therapy, though typically self-limited 1
Ensure adequate hydration to prevent crystalluria and renal toxicity 1, 2
Dose adjustment is required if renal insufficiency develops 1
Monitor renal function during treatment, particularly in children with longer duration of therapy 4
Treatment Failure and Resistance
If the child fails to respond after 5-7 days of appropriate acyclovir therapy, consider intravenous foscarnet 40 mg/kg per dose three times daily for acyclovir-resistant HSV 1, 2
For children with frequent or severe recurrences, daily suppressive therapy with oral acyclovir can be considered 1
Critical Pitfalls to Avoid
Do not use topical antivirals alone as they cannot reach the site of viral reactivation or impact the host immune response 1
Do not stop treatment early when symptoms improve; continue until complete healing occurs 1
Pediatric experience with oral acyclovir in children under 2 years is more limited than in older children, but available data support its safety and efficacy 1, 3