EVIDENCE-BASED ANSWER:
Daily oral acyclovir or valacyclovir may help prevent herpes simplex labialis (HSL) recurrences (strength of recommendation [SOR]: B, meta-analysis of randomized controlled trials [RCTs] with heterogeneous results).
No trials compare oral or topical treatments for HSL outbreaks against each other. Oral antivirals modestly reduce healing time and duration of pain, varying according to the agent used: valacyclovir reduces both healing time and duration of pain, famciclovir reduces both in one dosage form but not another, and acyclovir reduces only pain duration (SOR: B, single RCTs).
Several topical medications (acyclovir, penciclovir, docosanol) modestly decrease healing time and pain duration—typically by less than a day—and require multiple doses per day (SOR: B, multiple RCTs).
EVIDENCE SUMMARY
A systematic review and meta-analysis of the effectiveness of oral and topical nucleoside antiviral agents to prevent recurrent HSL in immunocompetent people found 11 RCTs with a total of 1250 patients that compared an active drug against placebo.1 The medications were topical 5% acyclovir, topical 1% penciclovir, and oral acyclovir, valacyclovir, or famciclovir in various doses. The primary outcome was recurrence of herpes simplex virus type 1 lesions during the treatment period. The relative risk (RR) of recurrence ranged from 0.22 to 1.22. Pooled results found a benefit favoring antiviral agents (RR of recurrence=0.70; 95% confidence interval [CI], 0.55-0.89).
Seven of the trials looked at acyclovir (5 oral, 2 topical). A subgroup analysis demonstrated that oral acyclovir (800-1000 mg/d) was more effective than placebo (RR=0.51; 95% CI, 0.29-0.88), whereas topical acyclovir wasn’t. Oral valacyclovir (2 studies; 500 mg/d for 4 months) also reduced recurrence (RR=0.65; 95% CI, 0.43-0.91). The authors of the meta-analysis noted that although 9 studies favored the use of an antiviral drug, only 4 showed statistically significant differences when compared with placebo, and none of them had a low risk of bias. They concluded that the review supported using oral acyclovir and valacyclovir to prevent recurrent HSL.1
Oral antivirals produce variable treatment results
Three RCTs evaluated oral antiviral medications against placebo to treat recurrent HSL, with mixed results. The largest RCT found that valacyclovir (2000 mg twice in 24 hours, with or without an additional 1000 mg twice in another 24 hours) modestly but significantly reduced both healing time and duration of pain (by 0.5-0.8 day).2 The second RCT showed that a higher, single dose of famciclovir (1500 mg) reduced healing time (by 1.8 days) and pain duration (by 1.2 days) and that a smaller, repeated dose (750 mg twice in 24 hours) reduced healing time alone (by 2.2 days).3