Abstract: A total of 26 trials (among which six had a cross-over design) were included. Among the 6950 randomly assigned participants, 54% (range 0 to100%) were female, mean age was 35 years (range 26 to 45.1), and the mean number of recurrences per year was 11 (range 6.3 to 17.8). Duration of treatment was two to 12 months. Risk of bias was considered high for half of the studies and unclear for the other half. A total of 14 trials compared acyclovir versus placebo, four trials compared valacyclovir versus placebo and 2 trials compared valacyclovir versus no treatment. Three trials compared famciclovir versus placebo. Two trials compared valacyclovir versus famciclovir and one trial compared acyclovir versus valacyclovir versus placebo. We analyzed data from 22 trials for the outcome: risk of having at least one clinical recurrence. We could not obtain the outcome data for four trials. In placebo-controlled trials, there was a low quality evidence that the risk of having at least one clinical recurrence was reduced with acyclovir (nine parallel-group trials, n = 2049; pooled RR 0.48, 95% confidence interval (CI) 0.39 to 0.58), valacyclovir (four trials, n = 1788; pooled RR 0.41, 95% CI 0.24 to 0.69), or famciclovir (two trials, n = 732; pooled RR 0.57, 95% CI 0.50 to 0.64). The six cross-over trials showed larger treatment effects on average than the parallel-group trials. We found evidence of a small-study effect for acyclovir placebo-controlled trials (adjusted pooled RR 0.61, 95% CI 0.49 to 0.75). In analyzing parallel-group trials by daily dose, no clear evidence was found of a dose-response relationship for any drug. In head-to-head trials, the risk of having at least one recurrence was increased with valacyclovir rather than acyclovir (one trial, n = 1345; RR 1.16, 95% CI 1.01 to 1.34) and was not significantly different from that seen with famciclovir as compared with valacyclovir (one trial, n = 320; RR 1.18, 95% CI 0.86 to 1.63). We included 16 parallel-arm trials in a network meta-analysis and we were unable to determine which of the drugs was most effective in reducing the risk of at least one clinical recurrence (after adjustment for small-study effects, pooled RR 0.83, 95% CI 0.61 to 1.11 for valacyclovir vs acyclovir; pooled RR 1.04, 95% CI, 0.71 to 1.49 for famciclovir vs acyclovir; and pooled RR 1.26, 95% CI 0.89 to 1.75 for famciclovir vs valacyclovir). Safety data were sought but were reported as total numbers of adverse events. Owing to risk of bias and inconsistency, there is low quality evidence that suppressive antiviral therapy with acyclovir, valacyclovir or famciclovir in pacients experiencing at least four recurrences of genital herpes per year decreases the number of pacients with at least one recurrence as compared with placebo. Network meta-analysis of the few direct comparisons and the indirect comparisons did not show superiority of one drug over another.

Plain-language summary: A total of 26 trials including 6950 patients were included in this review. Fifty-four percent of these patients were female, mean age was 35 years, and mean number of recurrences per year before entry into the trials was 11. Duration of treatment in trials ranged from two to 12 months. A total of 14 trials compared acyclovir versus placebo. Four trials compared valacyclovir versus placebo and two trials compared valacyclovir versus no treatment. Three trials compared famciclovir versus placebo. Two trials compared valacyclovir versus famciclovir, and one trial compared acyclovir versus valacyclovir versus placebo. Among the 26 included trials, 22 declared pharmaceutical company funding. The last search for studies was carried out in February 2014. Suppressive antiviral therapy with acyclovir, valacyclovir, or famciclovir in patients experiencing at least four recurrences per year decreases the number of patients having at least one recurrence compared with placebo. There is no evidence that suggests that any of these drugs is superior to the others. Althought the three antiviral drugs showed better results compared with placebo, we are uncertain as to how much a difference there are likely to make, because of issues with the conduct and reporting of studies, and inconsistency of their results. The quality of the evidence is low and we think that the size of the effects is likely to change with more research. Because few studies compared the three drugs against one other, we are moderately confident in the fact that there is no difference between the three drugs in terms of effectiveness.