What is the recommended dose of acyclovir (antiviral medication) for a 17-year-old patient?

Acyclovir Dosing for a 17-Year-Old

For a 17-year-old patient, acyclovir dosing depends on the specific indication, but for most herpes simplex infections, use adult dosing of 400 mg orally twice daily for genital herpes or 10 mg/kg IV every 8 hours for severe disease; for herpes zoster, use 800 mg orally 5 times daily. 1

Dosing by Clinical Indication

Genital Herpes (HSV)

• Oral therapy: 400 mg orally twice daily for 5-14 days 1
• This is the adult/adolescent dosing that applies to 17-year-olds
• Alternative: Valacyclovir 1 g orally twice daily is approved for adults and adolescents and may be used in older children able to receive adult dosing 1

Mucocutaneous HSV (Mild Gingivostomatitis)

• If patient weighs <45 kg: 20 mg/kg (max 400 mg/dose) orally 3 times daily for 5-10 days 1
• If patient weighs ≥45 kg or can take adult dosing: 400 mg orally twice daily for 5-14 days 1

Moderate to Severe HSV (Gingivostomatitis or Disseminated)

• IV therapy: 5-10 mg/kg IV every 8 hours 1
• Switch to oral acyclovir once lesions begin to regress and continue until complete healing 1

CNS or Disseminated HSV Disease

• IV therapy: 10 mg/kg IV every 8 hours for 21 days 1
• For severe disease requiring hospitalization (disseminated infection, pneumonitis, hepatitis, meningitis, or encephalitis): 5-10 mg/kg IV every 8 hours for 5-7 days or until clinical resolution 1

Herpes Zoster (Shingles)

• Oral therapy: 800 mg orally 5 times daily for 7-10 days 2
• For severe or disseminated disease: 10 mg/kg IV every 8 hours for 7-10 days 2

Suspected Viral Encephalitis

• For patients >12 years: 10 mg/kg IV every 8 hours 1
• For patients 3 months-12 years: 500 mg/m² IV every 8 hours 1
• Start within 6 hours of admission if viral encephalitis is suspected 1

Key Clinical Considerations

Weight-Based vs. Adult Dosing Decision Point

The critical threshold is 45 kg body weight for determining whether to use pediatric weight-based dosing or adult fixed dosing 1. Most 17-year-olds will qualify for adult dosing, but verify the patient's weight.

Renal Function Adjustment

• Reduce acyclovir dose in patients with pre-existing renal impairment 1
• Monitor for crystalluria and obstructive nephropathy, particularly with IV administration 1
• High doses require monitoring of renal function and neutrophil count 3

Route of Administration Selection

• Use IV therapy for: severe disease, complications requiring hospitalization, inability to tolerate oral medication, CNS involvement, or disseminated infection 1, 3
• Use oral therapy for: mild to moderate disease, genital herpes, uncomplicated mucocutaneous infections 1

Common Pitfalls to Avoid

• Don't delay treatment in suspected HSV encephalitis—start acyclovir within 6 hours even if diagnostic results are pending 1
• Don't underdose by using pediatric dosing in a 17-year-old who weighs ≥45 kg; use adult dosing 1
• Don't forget that acyclovir does not eradicate latent virus and does not affect recurrence risk after stopping medication 3
• Don't use empirical acyclovir for all encephalopathy without considering the differential diagnosis, as this can delay identification of other treatable causes 1