Is Bactroban (mupirocin) effective for treating cold sores?

Do Not Use Bactroban (Mupirocin) for Cold Sores

Bactroban (mupirocin) is a topical antibiotic indicated only for bacterial skin infections like impetigo and should never be used for cold sores, which are viral infections caused by herpes simplex virus (HSV-1). 1

Why Bactroban Is Inappropriate for Cold Sores

Wrong Mechanism of Action

• Mupirocin is an antibacterial agent that works against Staphylococcus aureus and Streptococcus species—it has zero antiviral activity against HSV-1. 1
• Cold sores are caused by herpes simplex virus, not bacteria, making antibacterial therapy completely ineffective for the underlying viral infection 2
• Topical mupirocin is specifically indicated for localized and nonbullous impetigo (bacterial skin infection), not viral lesions 1

Correct Treatment for Cold Sores

The evidence-based first-line treatment for cold sores is oral valacyclovir 2g twice daily for 1 day, initiated within 24 hours of symptom onset. 2, 3

Oral Antiviral Options (in order of preference):

• Valacyclovir 2g twice daily for 1 day (most convenient, FDA-approved, reduces episode duration by 1.0 day) 2, 4
• Famciclovir 1500mg as a single dose (alternative with similar efficacy) 2
• Acyclovir 400mg five times daily for 5 days (requires more frequent dosing but effective) 2, 3

Critical Timing Considerations:

• Treatment must be initiated within 24 hours of symptom onset, ideally during the prodromal stage (tingling, itching, burning) for maximum effectiveness 2, 3
• Peak viral titers occur in the first 24 hours after lesion onset, making early intervention essential 2
• Efficacy decreases significantly when treatment starts after lesions have fully developed 2

For Frequent Recurrences (≥6 Episodes Per Year)

Consider daily suppressive therapy with valacyclovir 500mg once daily, which reduces recurrence frequency by ≥75%. 2

Alternative suppressive options include:

• Famciclovir 250mg twice daily 2
• Acyclovir 400mg twice daily 2

Common Pitfalls to Avoid

• Never use topical antibiotics like mupirocin for viral infections—they provide no benefit and may delay appropriate antiviral treatment 1
• Avoid relying solely on topical antivirals—oral therapy is significantly more effective than topical treatments, which provide only modest clinical benefit 2
• Do not start treatment too late—waiting until lesions are fully developed substantially reduces treatment efficacy 2
• Topical antivirals are ineffective for suppressive therapy since they cannot reach the site of viral reactivation in sensory ganglia 2

When Secondary Bacterial Infection Occurs

The only scenario where mupirocin might be considered is if a cold sore becomes secondarily infected with bacteria (rare), showing signs of purulent drainage, expanding erythema, or cellulitis—but this would be in addition to, not instead of, antiviral therapy 1