What is the recommended dose of acyclovir (antiviral medication) for an 11-year-old pediatric patient with herpes zoster?

Acyclovir Dosing for Pediatric Herpes Zoster

For an 11-year-old child with herpes zoster, administer acyclovir 800 mg orally five times daily for 7-10 days, starting within 72 hours of rash onset for maximum efficacy. 1, 2

Recommended Dosing Regimen

• The CDC recommends acyclovir 800 mg orally five times daily for herpes zoster in adolescents and older children, which provides higher total daily exposure than weight-based dosing and is the preferred regimen 1

• While weight-based dosing of 20 mg/kg per dose (maximum 800 mg) four times daily can be used, the five-times-daily adult regimen is superior because varicella-zoster virus requires higher drug exposure than herpes simplex virus 1, 3

• For an 11-year-old, the 800 mg five-times-daily regimen is appropriate as this age group can typically receive adult dosing 1, 2

Treatment Timing and Duration

• Initiate treatment within 72 hours of rash onset—ideally within 48 hours—for maximum benefit 1

• Continue therapy for 7-10 days 1, 2

• Clinical improvement should be evident within 48-72 hours of starting treatment 1

When to Use Intravenous Therapy

• Switch to IV acyclovir 10 mg/kg every 8 hours (or 500 mg/m² every 8 hours for children >1 year) if the patient develops: 1, 3

  • Severe disease requiring hospitalization
  • Disseminated infection
  • Complications such as encephalitis or visceral involvement
  • Inability to tolerate oral medications

• Continue IV therapy for 5-7 days or until clinical resolution, then may transition to oral therapy 1

Critical Safety Considerations

• Ensure adequate hydration throughout treatment to prevent acyclovir crystalluria, as this is the most important preventable adverse effect 1, 3

• Monitor mental status, particularly in patients with any degree of renal impairment, as CNS adverse events (confusion, hallucinations) can occur 2

• Adjust dosing downward if renal function is impaired 2, 3

Alternative Agent for Adolescents

• Famciclovir 500 mg orally three times daily for 7-10 days is an alternative for adolescents who can receive adult dosing, though pediatric data are limited 1

Common Pitfalls to Avoid

• Do not use topical acyclovir—it is substantially less effective than oral therapy and should not be used for systemic infections 1

• Do not delay treatment waiting for laboratory confirmation; herpes zoster is a clinical diagnosis and early treatment is critical 1

• Remember that acyclovir does not eradicate latent virus or prevent postherpetic neuralgia with certainty, though it may reduce its duration 1, 3, 4

• The bioavailability of oral acyclovir decreases with increasing dose, which is why the five-times-daily regimen is necessary to maintain adequate drug levels 2