What is the recommended dose of acyclovir (antiviral medication) for treating herpes simplex virus (HSV) and varicella-zoster virus (VZV) infections in adolescents with normal renal function?

Acyclovir Dosing in Adolescents

For adolescents with normal renal function, acyclovir dosing depends on the specific viral infection being treated, with genital HSV requiring 200-400 mg orally 5 times daily or 800 mg twice daily, while chickenpox requires 20 mg/kg (maximum 800 mg) orally 4 times daily for 7-10 days. 1

Herpes Simplex Virus (HSV) Infections

First Episode Genital Herpes

• Acyclovir 200 mg orally 5 times daily for 7-10 days until clinical resolution is achieved 1
• For herpes proctitis specifically, increase to 400 mg orally 5 times daily for 10 days 1

Recurrent Genital Herpes Episodes

Adolescents have three equivalent dosing options 1:

• 200 mg orally 5 times daily for 5 days, OR
• 400 mg orally 3 times daily for 5 days, OR
• 800 mg orally twice daily for 5 days

The higher-dose, less-frequent regimens improve adherence while maintaining equivalent efficacy 1

Suppressive Therapy for Frequent Recurrences

• Primary regimen: 400 mg orally twice daily for patients with ≥6 recurrences per year 1
• Alternative: 200 mg orally 3-5 times daily, titrated to the lowest effective dose 1
• Reassess need for continuation after 1 year of therapy 1

Herpetic Gingivostomatitis

• 20 mg/kg per dose (maximum 400 mg) orally 3 times daily for 5-10 days, initiated within the first 3 days of symptom onset 2
• Monitor for clinical improvement within 48-72 hours 2

Varicella-Zoster Virus (VZV) Infections

Chickenpox (Varicella)

• Acyclovir 20 mg/kg orally per dose (maximum 800 mg/dose) 4 times daily for 7-10 days or until no new lesions appear for 48 hours 1
• This dosing applies to adolescents with no or moderate immunosuppression 1

Herpes Zoster (Shingles)

• For adolescents who can receive adult dosing, valacyclovir 1 gram orally 3 times daily for 7 days is preferred over acyclovir due to improved bioavailability and less frequent dosing 3
• If using acyclovir, the equivalent dose would be 800 mg orally 5 times daily for 7-10 days (extrapolated from adult data) 3

Severe or Complicated Infections

Intravenous Therapy Indications

For severe disease requiring hospitalization (disseminated infection, encephalitis, pneumonitis, hepatitis) 1:

• Acyclovir 5-10 mg/kg IV every 8 hours for 5-7 days until clinical resolution 1
• Some experts use body surface area dosing: 500 mg/m² IV every 8 hours for children >1 year 1

Eczema Herpeticum

• Mild disease: 20 mg/kg orally (maximum 400 mg/dose) 3 times daily for 5-10 days 4
• Moderate to severe: 5-10 mg/kg IV every 8 hours, then transition to oral therapy once lesions regress 4

Alternative Agents for Adolescents

Valacyclovir

• FDA-approved for adolescents ≥12 years for cold sores 3
• For chickenpox in adolescents ≥12 years: 20 mg/kg orally 3 times daily (maximum 1 gram/dose) for 5 days 3
• Valacyclovir offers superior bioavailability and less frequent dosing compared to acyclovir 3

Famciclovir

• Approved for adolescents with zoster: 500 mg orally 3 times daily for 7-10 days 1
• Limited pediatric data; reserved for adolescents who can receive adult dosing 1

Critical Monitoring and Safety Considerations

Renal Function

• Ensure adequate hydration throughout treatment to prevent acyclovir crystalluria 4, 2
• Dose reduction required for renal impairment 3
• Elderly patients and those with renal dysfunction are at higher risk for CNS adverse events 3

Treatment Response

• Expect clinical improvement within 48-72 hours of initiating therapy 4, 2
• Watch for neutropenia with prolonged use, though uncommon with standard 5-10 day courses 4, 2, 5

Acyclovir-Resistant HSV

• For treatment failure or confirmed resistance: foscarnet 40-60 mg/kg IV every 8 hours for 7-10 days 1, 2

Common Pitfalls to Avoid

• Topical acyclovir is substantially less effective than oral therapy and should not be used for systemic infections 1
• Acyclovir does not eradicate latent virus or prevent future recurrences after discontinuation 1, 5
• Early initiation is critical—treatment is most effective when started within 72 hours of symptom onset for VZV and within 3 days for HSV gingivostomatitis 2, 3
• Do not use valacyclovir for genital herpes in children <12 years—insufficient efficacy data in this population 3