What is the recommended dose of acyclovir (antiviral medication) for treating herpes zoster?

Acyclovir Dosing for Herpes Zoster

For herpes zoster (shingles), the recommended dose is acyclovir 800 mg orally 5 times daily for 7-10 days, initiated within 72 hours of rash onset for maximum benefit. 1, 2, 3

Oral Therapy Regimen

Standard Dosing

• Acyclovir 800 mg orally 5 times daily for 7-10 days is the established regimen for immunocompetent adults with herpes zoster 1, 2, 3
• The 800 mg dose is superior to lower doses (400 mg showed no significant benefit over placebo) 3
• Treatment must be started within 72 hours of rash onset; starting after 48 hours significantly reduces efficacy 2

Clinical Benefits of Treatment

• Accelerates resolution of rash with faster time to crusting and healing 1, 2, 3
• Reduces duration and severity of acute pain during the first 2-10 days of treatment 2, 3
• Decreases new lesion formation and prevents dissemination to adjacent dermatomes 1, 3
• May reduce the prevalence of post-herpetic neuralgia in the first 3 months, though this benefit is modest 1, 3

Intravenous Therapy for Severe Disease

When to Use IV Acyclovir

• For severe disease, complications, or hospitalized patients: acyclovir 5-10 mg/kg IV every 8 hours for 5-7 days or until clinical improvement 4
• IV therapy is indicated for immunocompromised patients, disseminated zoster, or CNS involvement 5
• The higher dose (10 mg/kg) is preferred given that varicella-zoster virus is less sensitive to acyclovir than herpes simplex virus 5

Critical Safety Considerations with IV Therapy

• Maintain adequate hydration and urine flow to prevent crystalluria 5
• Monitor mental status as neurotoxicity can occur 5
• Adjust dosing downward in renal impairment 5

Alternative Agent: Valacyclovir

• Valacyclovir 1000 mg orally 3 times daily for 7 days offers superior convenience with equivalent or better efficacy compared to acyclovir 6
• Valacyclovir provides 3-5 fold higher bioavailability than acyclovir, allowing less frequent dosing 6
• It significantly accelerates resolution of pain (median 38 days vs 51 days with acyclovir) and reduces post-herpetic neuralgia duration 6

Special Populations

Immunocompromised Patients

• Require more aggressive therapy with higher doses or IV administration 7, 4
• May need suppressive therapy with acyclovir 400 mg orally 3-5 times daily 4
• Higher risk of acyclovir-resistant strains, which require foscarnet 40 mg/kg IV 3 times daily or 60 mg/kg IV twice daily 4

Common Pitfalls to Avoid

• Never use topical acyclovir for herpes zoster—it is substantially less effective than oral therapy 7
• Do not delay treatment beyond 72 hours of rash onset, as efficacy drops significantly 2
• The 400 mg dose is inadequate for herpes zoster (unlike herpes simplex) and should not be used 3
• Acyclovir does not eradicate latent virus and does not prevent future recurrences 7