Aciclovir Dosing for Herpes Zoster
For immunocompetent adults with herpes zoster, treat with aciclovir 800 mg orally five times daily for 7-10 days, initiated within 72 hours (ideally within 48 hours) of rash onset 1.
Adult Dosing by Clinical Scenario
Immunocompetent Adults (Standard Cases)
- Oral aciclovir 800 mg five times daily for 7-10 days 1
- Must initiate within 72 hours of rash onset for maximum benefit
- Greatest efficacy when started within 48 hours 2
- This regimen significantly reduces viral shedding, accelerates healing, decreases new lesion formation, and reduces acute pain severity 3, 2
- May reduce postherpetic neuralgia incidence by 46% at 6 months 4
Important caveat: The 800 mg five times daily dose is superior to lower doses (400 mg five times daily showed no significant benefit over placebo) 3.
Severe Disease or Complications
- Aciclovir 5-10 mg/kg IV every 8 hours for 5-7 days until clinical resolution 1
- Use IV route for:
- Disseminated infection
- CNS involvement (encephalitis)
- Visceral involvement (pneumonitis, hepatitis)
- Patients requiring hospitalization
Immunosuppressed Adults (HIV-infected or other immunocompromise)
- Aciclovir 10 mg/kg IV every 8 hours for severe immunosuppression 5
- For patients not responding to aciclovir: Foscarnet 40-60 mg/kg IV three times daily for 7-10 days 5
- Alternative oral option for adolescents/adults: Famciclovir 500 mg orally three times daily for 7-10 days 5
Pediatric Dosing
HIV-Infected or Immunocompromised Children
Mild to moderate immunosuppression:
- Aciclovir 20 mg/kg orally (maximum 800 mg/dose) four times daily for 7-10 days or until no new lesions for 48 hours 5
Severe immunosuppression:
- Aciclovir 10 mg/kg IV three times daily 5
- Some experts use body surface area dosing: 500 mg/m² IV every 8 hours in children >1 year 5
Immunocompetent Children with Chickenpox (Varicella)
- Aciclovir 20 mg/kg orally (maximum 800 mg/dose) four times daily for 5 days 1
- Children >40 kg: use adult dose of 800 mg four times daily 1
- Must initiate within 24 hours of rash onset 1
- Note: Intravenous aciclovir is indicated for varicella in immunocompromised children 1, 6
For immunocompromised children with varicella/zoster: 10 mg/kg IV every 8 hours for 5 days effectively prevents visceral involvement and is well-tolerated 6, 7.
Renal Dose Adjustments
Critical consideration: Aciclovir requires dose modification in renal impairment 1.
| Creatinine Clearance | Standard Dose | Adjusted Dose | Interval |
|---|---|---|---|
| >25 mL/min | 800 mg 5x daily | 800 mg | Every 4 hours |
| 10-25 mL/min | 800 mg 5x daily | 800 mg | Every 8 hours |
| 0-10 mL/min | 800 mg 5x daily | 800 mg | Every 12 hours |
Hemodialysis patients: Administer additional dose after each dialysis session due to 60% reduction in plasma concentrations during 6-hour dialysis 1.
Geriatric patients: Higher plasma concentrations occur due to age-related renal decline; dose reduction required if underlying renal impairment present 1.
Key Clinical Pearls
- Timing is critical: Treatment initiated >72 hours after rash onset has minimal benefit
- Food doesn't matter: Aciclovir can be taken with or without food 1
- Bioavailability decreases with dose: The 800 mg dose has lower bioavailability than smaller doses, but remains clinically superior 1, 3
- Ocular involvement: Requires ophthalmology consultation 5
- Aciclovir resistance: If suspected (particularly in immunocompromised patients with prolonged disease), switch to foscarnet 5
The evidence strongly supports the 800 mg five times daily regimen over lower doses, with multiple placebo-controlled trials demonstrating significant clinical benefit in reducing acute symptoms and potentially preventing postherpetic neuralgia 3, 2, 4.