Acyclovir Dosing for Genital Herpes in Children
For children with genital herpes weighing less than 45 kg, administer acyclovir 20 mg/kg per dose (maximum 400 mg/dose) orally three times daily for 5-14 days. 1
Weight-Based Dosing Algorithm
Children <45 kg
- Acyclovir 20 mg/kg per dose orally three times daily (maximum 400 mg/dose) 1
- Duration: 5-14 days 1
- Continue therapy until lesions completely heal 1
Adolescents ≥45 kg and Adults
- Acyclovir 400 mg orally twice daily for 5-14 days 1
- Alternative FDA-approved regimen: 200 mg every 4 hours, 5 times daily for 10 days (first episode) 2
Treatment Duration Considerations
The CDC guidelines specify a range of 5-14 days, with the specific duration determined by disease severity: 1
- First episode genital herpes: Treat for 7-10 days or until clinical resolution 3
- Recurrent episodes: 5 days is typically sufficient 2
- Severe disease: May require up to 14 days 1
Critical Implementation Points
Timing of Initiation
- Start 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 4
- Clinical improvement should be monitored within 48-72 hours 5, 4
Monitoring and Safety
- Ensure adequate hydration throughout treatment to prevent acyclovir crystalluria 5, 4
- Monitor renal function, particularly with prolonged use 1
- Watch for neutropenia with extended therapy (21-46% in prolonged courses, though typically self-limited) 4
Common Pitfalls to Avoid
- Do not stop treatment when symptoms improve—continue until complete healing occurs 5, 4
- Do not use topical acyclovir alone as it cannot reach the site of viral reactivation or impact the host immune response 4
- Do not underdose based on adult dosing—children require weight-based dosing due to different pharmacokinetics 6
Treatment Failure or Resistance
If the child fails to respond after 5-7 days of appropriate acyclovir therapy: 4
- Consider foscarnet 40 mg/kg IV three times daily for acyclovir-resistant HSV 1, 4
- Alternative: foscarnet 60 mg/kg IV twice daily 1
Special Populations
Neonates with Genital HSV
- Higher doses required: Acyclovir 20 mg/kg IV every 8 hours 4
- Neonatal HSV requires 14-21 days of IV therapy depending on disease extent 4
Renal Impairment
- Dose adjustment required based on creatinine clearance 2
- For creatinine clearance 0-10 mL/min: 200 mg every 12 hours 2
Evidence Quality
These recommendations carry an AI rating (strong evidence from randomized controlled trials) from the CDC, National Institutes of Health, HIV Medicine Association of the Infectious Diseases Society of America, Pediatric Infectious Diseases Society, and American Academy of Pediatrics. 1 The weight-based dosing of 20 mg/kg three times daily represents the consensus standard for pediatric genital herpes treatment across all major guideline bodies. 1, 4