Acyclovir 400 mg Five Times Daily is NOT the Recommended Dose for Shingles
For herpes zoster (shingles), the correct acyclovir dose is 800 mg orally five times daily for 7-10 days, not 400 mg. 1
Correct Dosing for Shingles
Standard Immunocompetent Patients
- Acyclovir 800 mg orally 5 times daily for 7-10 days is the established regimen for herpes zoster 1
- This is four times higher than the 400 mg dose mentioned in your question 1
- The 400 mg dosing (either 3 or 5 times daily) is appropriate only for herpes simplex infections (cold sores or genital herpes), not shingles 2, 3
Immunocompromised Patients
- For immunocompromised patients including those with HIV, the same 800 mg orally 5 times daily for 7-10 days is recommended 1
- Some experts use body surface area-based dosing: 500 mg/m² every 8 hours 1
- For severe or disseminated disease, intravenous acyclovir 10 mg/kg every 8 hours for 7-10 days is indicated 1
Why the Higher Dose Matters
The varicella-zoster virus (VZV) that causes shingles requires substantially higher drug concentrations than herpes simplex virus to achieve adequate viral suppression 4. Using the lower 400 mg dose would result in:
- Inadequate viral suppression
- Prolonged acute symptoms
- Potentially increased risk of postherpetic neuralgia
- Suboptimal clinical outcomes
Alternative Treatment Options with Better Convenience
If the five-times-daily dosing is problematic for adherence:
- Famciclovir 500 mg three times daily for 7-10 days offers comparable efficacy with more convenient dosing 1, 5
- Valacyclovir 1000 mg three times daily for 7 days provides similar or superior efficacy to acyclovir with easier dosing 6, 7
Critical Timing Considerations
- Treatment should ideally be initiated within 72 hours of rash onset for maximum benefit 4
- Starting therapy after 48-72 hours significantly reduces effectiveness for acute symptoms 4
- However, treatment may still provide benefit for pain reduction even when started later than 72 hours 6
Common Pitfall to Avoid
Do not confuse herpes simplex dosing with herpes zoster dosing. The 400 mg dose is appropriate for herpes simplex (cold sores, genital herpes) but grossly inadequate for shingles 2, 3, 1. This is a frequent prescribing error that can lead to treatment failure.