What is the recommended dose of Acyclovir (antiviral medication) for an adult patient with herpes zoster (shingles) and normal renal function?

Acyclovir Dosing for Herpes Zoster in Adults with Normal Renal Function

For immunocompetent adults with uncomplicated herpes zoster and normal renal function, the recommended dose is acyclovir 800 mg orally five times daily for 7-10 days, continuing until all lesions have completely scabbed. 1

Standard Oral Dosing Regimen

• Acyclovir 800 mg orally five times daily is the established dose for herpes zoster, significantly higher than doses used for herpes simplex infections 2, 3
• Treatment duration is 7-10 days minimum, but must continue until all lesions have completely scabbed—this is the critical clinical endpoint, not an arbitrary calendar duration 1
• Therapy should be initiated within 72 hours of rash onset for optimal efficacy in reducing acute pain, accelerating lesion healing, and preventing postherpetic neuralgia 1

The high dose requirement (800 mg five times daily) reflects the fact that varicella zoster virus is considerably less sensitive to acyclovir than herpes simplex virus, necessitating higher plasma concentrations to achieve therapeutic effect 2.

Alternative Oral Antiviral Options

While acyclovir remains effective, valacyclovir 1000 mg three times daily for 7 days offers superior convenience with equivalent or better efficacy 4:

• Valacyclovir provides 3-5 fold higher bioavailability than acyclovir 4
• Significantly accelerates resolution of zoster-associated pain (median 38 days vs 51 days with acyclovir, p=0.001) 4
• Reduces duration of postherpetic neuralgia and decreases proportion of patients with pain persisting at 6 months (19.3% vs 25.7%) 4

Famciclovir 500 mg three times daily for 7 days is equally effective with comparable outcomes to acyclovir 5.

When to Escalate to Intravenous Therapy

Intravenous acyclovir 10 mg/kg every 8 hours is mandatory for 1, 6, 2:

• Disseminated herpes zoster (multi-dermatomal involvement, visceral complications)
• Immunocompromised patients with severe disease
• CNS involvement (encephalitis, meningitis)
• Complicated ophthalmic disease (herpes zoster ophthalmicus with vision-threatening features)
• Severe disease requiring hospitalization

IV therapy should continue for 7-14 days and until clinical resolution is achieved 6.

Critical Monitoring and Dosing Considerations

• Adequate hydration and urine flow must be maintained at these high doses to prevent acyclovir crystalluria and nephrotoxicity 2
• Monitor renal function at initiation and once or twice weekly during treatment 1
• Mental status monitoring is essential, as high-dose acyclovir can rarely cause neurotoxicity 2
• Renal dose adjustments are mandatory for any degree of renal impairment—failure to adjust can lead to serious toxicity 6, 2

Common Pitfalls to Avoid

• Do not use topical acyclovir—it is substantially less effective than systemic therapy and is not recommended for herpes zoster 1
• Do not stop treatment at exactly 7 days if lesions are still forming or have not completely scabbed; continue until all lesions have crusted 1
• Do not use genital herpes dosing (400 mg three times daily)—this is grossly inadequate for varicella zoster virus 1
• Do not delay treatment beyond 72 hours of rash onset, as efficacy diminishes significantly 1

Special Population Considerations

For immunocompromised patients with uncomplicated herpes zoster, higher oral doses may be needed (acyclovir 400 mg orally 3-5 times daily until clinical resolution), though many experts prefer IV therapy for this population given the high risk of dissemination 1.

For acyclovir-resistant cases (suspected when lesions fail to resolve after 7-10 days of appropriate therapy), switch to foscarnet 40 mg/kg IV every 8 hours until clinical resolution 1.