Acyclovir Dosage for Fever Blisters (Herpes Labialis)
For fever blisters (herpes labialis), the CDC recommends acyclovir 800 mg orally twice daily for 5 days, which offers the best balance of efficacy and convenience while maintaining equivalent clinical outcomes to more frequent dosing regimens. 1
Standard Treatment Regimens
The CDC provides three equally effective oral acyclovir regimens for treating cold sores, all administered for 5 days: 1, 2
- Acyclovir 800 mg orally twice daily - Most convenient option with best adherence 1
- Acyclovir 400 mg orally three times daily 1, 3, 2
- Acyclovir 200 mg orally five times daily 1, 2
The 800 mg twice-daily regimen demonstrates superior clinical outcomes including shorter symptom duration (8.1 days vs 12.5 days with placebo), reduced pain duration (2.5 days vs 3.9 days), and fewer lesions developing (7% vs 26% with placebo). 1
Critical Timing for Treatment Initiation
Treatment must be initiated during the prodrome or within 2 days of lesion onset for maximum benefit. 1, 2 Starting therapy after this window significantly reduces effectiveness, and most immunocompetent patients with recurrent disease experience limited benefit from delayed therapy. 1, 2 Patients should begin treatment at the first sign of tingling, burning, or itching before visible lesions appear. 4
Special Populations and Circumstances
Immunocompromised Patients
For HIV-infected or otherwise immunocompromised patients, higher doses are required: 2
- Acyclovir 400 mg orally 3-5 times daily until clinical resolution 3, 2
- For severe cases requiring hospitalization: Acyclovir 5-10 mg/kg IV every 8 hours 3, 2
Frequent Recurrences (≥6 Episodes Per Year)
For patients with frequent recurrences, suppressive therapy should be considered: 3, 5
- Acyclovir 400 mg orally twice daily for chronic suppression 3, 2
- This reduces recurrence frequency by ≥75% and results in a 53% reduction in clinical recurrences and 71% reduction in virus culture-positive recurrences 3, 5
Important Clinical Considerations
Oral acyclovir is significantly more effective than topical formulations for treating cold sores. 1, 2 Topical acyclovir only shortens lesion duration by approximately one day and is not effective for prevention of recurrent episodes. 6, 7
Key Patient Counseling Points
- Acyclovir neither eradicates latent virus nor affects subsequent risk, frequency, or severity of recurrences after discontinuation 1, 2
- Patients should abstain from activities that might spread the virus while lesions are present 1
- Adequate hydration is essential as acyclovir is primarily renally excreted and requires dose adjustment in renal insufficiency 3
Common Pitfalls to Avoid
- Do not delay treatment - waiting beyond 48 hours from onset significantly reduces effectiveness 1, 2
- Do not prescribe topical acyclovir as first-line therapy - oral formulations are significantly superior 1, 2
- Do not use high-dose valacyclovir (8 g/day) in immunosuppressed patients due to risk of hemolytic-uremic syndrome or thrombotic thrombocytopenic purpura 3