Acyclovir Dosing for Herpes Labialis
For herpes labialis (cold sores), prescribe acyclovir 400 mg orally three times daily for 5 days, initiated during the prodrome or within 2 days of lesion onset. 1
Recommended Dosing Regimens
The CDC provides three equally effective oral acyclovir options for treating recurrent herpes labialis, all for 5-day duration: 1, 2
- Acyclovir 400 mg orally 3 times daily for 5 days (preferred for balance of efficacy and convenience) 1, 2
- Acyclovir 200 mg orally 5 times daily for 5 days 1, 2
- Acyclovir 800 mg orally twice daily for 5 days 1, 2
The 800 mg twice-daily regimen offers superior convenience and adherence while maintaining equivalent efficacy, reducing symptom duration from 12.5 to 8.1 days (p=0.02) and pain duration from 3.9 to 2.5 days (p=0.02). 1
Critical Timing for Treatment Initiation
Treatment must be initiated during the prodrome or within 2 days of lesion onset for maximum benefit. 1 Starting therapy after this window significantly reduces effectiveness. 1 In clinical trials, 97% of patients who achieved benefit started treatment within 1 hour of first symptoms. 3
For patients who can reliably start treatment during prodrome or erythema stage, acyclovir reduces pain duration by 36% (p=0.02) and healing time by 27% (p=0.03). 3
Clinical Outcomes and Efficacy
Oral acyclovir demonstrates several measurable benefits: 3
- Reduces viral shedding (25% positive cultures vs 48% with placebo, p=0.004) 3
- Hastens lesion resolution when started early 3
- Does not prevent lesion development but accelerates healing 3
Important Caveats and Patient Counseling
Patients must understand that acyclovir neither eradicates latent virus nor affects subsequent risk, frequency, or severity of recurrences after discontinuation. 1 Most immunocompetent patients with recurrent disease experience limited benefit from therapy. 1
Patients should abstain from activities that might spread the virus while lesions are present, though transmission can occur during asymptomatic periods. 1
Topical Therapy: Not Recommended as Primary Treatment
Topical acyclovir (5% cream/ointment) is significantly less effective than oral formulations and provides no improvement in systemic symptoms. 1, 4 While topical formulations may increase abortive lesions when applied during prodrome, they shorten lesion duration by only about one day. 5, 6
Alternative Oral Antivirals (More Convenient but More Expensive)
If improved convenience is desired: 1
- Valacyclovir 2 g twice daily for 1 day provides comparable efficacy with superior convenience 1
- Famciclovir 1500 mg single dose significantly reduces healing time (4.4 vs 6.2 days with placebo, p<0.001) 1
These agents have greater oral bioavailability and require less frequent dosing but are more expensive and not approved for children. 4
Chronic Suppressive Therapy
For patients with frequent recurrences (≥6 episodes per year), consider acyclovir 400 mg orally twice daily for suppressive therapy, which reduces recurrence frequency by ≥75%. 2