What is the dosage instruction for acyclovir (400 mg) for an immunocompetent adult or adolescent with occasional cold sores?

Acyclovir 400 mg Dosing for Occasional Cold Sores

For occasional cold sores (herpes labialis), take acyclovir 400 mg orally three times daily for 5 days, starting at the first sign of symptoms or within 2 days of lesion onset. 1, 2

Standard Treatment Regimen

The CDC provides three equally effective dosing options for episodic treatment of cold sores, all for 5-day duration: 3, 1, 2

• Acyclovir 400 mg orally three times daily for 5 days 3, 1, 2
• Acyclovir 200 mg orally five times daily for 5 days 3, 1, 2
• Acyclovir 800 mg orally twice daily for 5 days 3, 1, 2

The 400 mg three times daily regimen offers a balance between efficacy and convenience compared to the more frequent 200 mg dosing. 1, 2

Critical Timing for Maximum Benefit

• Treatment must be initiated during the prodrome (tingling, burning sensation) or within 2 days of lesion onset for maximum effectiveness. 1, 2
• Starting therapy after this window significantly reduces treatment benefit. 1
• Most immunocompetent patients with recurrent disease experience limited benefit from delayed therapy. 1, 2

Important Patient Counseling Points

• Acyclovir neither eradicates latent virus nor affects the subsequent risk, frequency, or severity of future recurrences after discontinuation. 1, 2
• Patients should avoid close contact and activities that might spread the virus while lesions are present, though transmission can occur during asymptomatic periods. 1, 2
• Oral acyclovir is significantly more effective than topical formulations for treating cold sores. 1, 2

Alternative Considerations

If the 400 mg three times daily regimen is difficult for adherence, the 800 mg twice daily option may improve compliance due to less frequent dosing while maintaining equivalent efficacy. 1, 2

For patients seeking even greater convenience, valacyclovir 2 g twice daily for 1 day provides comparable efficacy with superior convenience, though this requires a different prescription. 1, 4

Common Pitfall to Avoid

Do not confuse this episodic treatment regimen with suppressive therapy. The 400 mg twice daily dosing is reserved for daily suppressive therapy in patients with frequent recurrences (≥6 episodes per year), not for treating individual outbreaks. 3, 2