Famciclovir Dosage for Cold Sores (Herpes Labialis)
For immunocompetent adults with cold sores, famciclovir should be given as a single 1500 mg dose initiated at the first sign or symptom (tingling, itching, burning, pain, or lesion). 1
Standard Dosing Regimen
- The FDA-approved dosage is 1500 mg as a single dose for recurrent herpes labialis in immunocompetent adults 1
- Treatment must be initiated at the earliest sign of cold sore development (prodrome phase) for maximum benefit 1
- This single-dose regimen can be taken with or without food 1
Clinical Efficacy
- The 1500 mg single-dose regimen significantly reduces median healing time to 4.4 days compared to 6.2 days with placebo (p<0.001) 2
- An alternative twice-daily regimen (750 mg twice daily for 1 day) also demonstrates efficacy, with healing time of 4.0 days versus 6.2 days with placebo (p<0.001) 2
- Both regimens reduce lesion size in a dose-proportional manner compared to placebo 2
Special Populations
HIV-Infected Patients
- For HIV-infected patients with recurrent orolabial herpes, the dosage is 500 mg twice daily for 7 days (not the single-dose regimen) 1
- This extended regimen is necessary because immunocompromised patients may have prolonged and more severe episodes 2
Renal Impairment
For patients with reduced kidney function, adjust the single-dose regimen as follows 1:
- CrCl ≥60 mL/min: 1500 mg single dose (standard)
- CrCl 40-59 mL/min: 750 mg single dose
- CrCl 20-39 mL/min: 500 mg single dose
- CrCl <20 mL/min: 250 mg single dose
- Hemodialysis patients: 250 mg single dose following dialysis
Comparison with Alternative Antivirals
While famciclovir offers convenient single-dose therapy, valacyclovir provides comparable efficacy with 2 grams twice daily for 1 day (taken 12 hours apart), achieving median episode duration of 4.0-5.0 days 2, 3. Both agents are superior to acyclovir in terms of dosing convenience, though acyclovir remains effective when given as 800 mg twice daily for 3-7 days 2.
Critical Timing Consideration
The single most important factor for efficacy is early initiation—treatment started during the prodromal phase or within the first hours of lesion appearance provides maximum benefit 1, 2. Delayed treatment significantly reduces the effectiveness of all antiviral regimens for cold sores.