Prophylactic chemotherapy with acyclovir for recurrent herpes simplex labialis

The medical literature was reviewed and 11 clinical trials of prophylactic topical or peroral acyclovir for the suppression of recurrent herpes simplex labialis were identified. The results of these trials showed that prophylactic topical acyclovir was mostly ineffective, but that prophylactic peroral acyclovir, in doses ranging from 400 to 1,000 mg/day, reduced the frequency of herpes labialis during treatment by 50-78%. The reduction in the frequency of episodes of herpes labialis with acyclovir prophylaxis is less than the suppressive effect that has been reported for herpes genitalis (50-78% vs. 80-90%). In trials of prophylactic acyclovir for herpes labialis induced by experimental ultraviolet radiation, 26% of induced lesions developed within 48 hours of radiation exposure ("immediate" lesions) and, in contrast to "delayed" lesions that developed 2-7 days post-irradiation, were not suppressed by the antiviral compound. It is proposed that these treatment-unresponsive immediate lesions have an atypical pathogenesis, possibly involving latency of herpes simplex virus in the labial epithelium, and that these may be responsible for the apparent difference between herpes labialis and genitalis in the degree of benefit from prophylactic acyclovir therapy.