The lesions of herpes simplex labialis often reach maximal severity and size within eight hours of the onset of symptoms. Given this narrow window of opportunity, successful treatment depends on patients being vigilant for the onset of prodromal symptoms and on the availability of effective therapy with a rapid onset of action. Spruance and colleagues evaluated three dosages of oral famciclovir against placebo in the treatment of herpes labialis induced by exposure to UV radiation.

A total of 243 healthy subjects with a history of herpes labialis induced by sunlight were recruited for the study, which was conducted at five academic medical centers. Most of the subjects were white women. They ranged from 18 to 68 years of age (mean age: 35 years), and the mean duration of herpes labialis was 20 years. The mean number of outbreaks in the previous year was 4.7.

For each patient, half of the lip area was exposed to four minimal erythema doses (MED) of UV radiation. The rest of the lip area and perioral skin were protected by sunscreen with a sun protection factor of 15. The subjects were randomly assigned to receive placebo or 125 mg, 250 mg or 500 mg of oral famciclovir three times daily for five days. They began taking the study medication 48 hours after UV exposure and returned to the clinic for assessment within seven days. If lesions developed, patients were seen daily until hard crusts developed, then every other day until loss of crusts. Final assessments of the subjects were conducted 13 to 15 days after UV exposure. Size of lesions, discomfort and other symptoms were recorded in patient diaries throughout the study.

Primary herpes lesions developed in 102 (42 percent) of the patients between 48 hours and seven days after UV exposure. Of these subjects, 87 had primary delayed classic lesions and 15 had primary delayed aborted lesions. Although delayed primary lesions occurred less frequently in the subjects who received famciclovir than in those who received placebo, the difference between the treated and placebo groups (39 percent versus 52 percent) was not statistically significant.

A dose-related reduction in the maximal lesion size was noted with famciclovir therapy, and the differences were statistically significant. With placebo, the maximal lesion size was 139 mm². With famciclovir, maximal lesion sizes were 105 mm², 77 mm² and 55 mm² at dosages of 125 mg, 250 mg and 500 mg, respectively.

The median time to healing of lesions as judged by both the clinical investigators and the subjects was significantly less in patients receiving the 500-mg dosage of famciclovir than for those receiving placebo. Healing took a median of four days in the subjects who received the 500-mg dosage of the antiviral agent, compared with a median of six days in the control subjects. There was a trend toward a reduction in pain with increasing dosages of famciclovir, but the differences did not reach statistical significance.

No statistically significant differences in adverse reactions were recorded between treatment groups. Headache and nausea occurred in less than 5 percent of the subjects.

The authors conclude that 500 mg of famciclovir three times daily resulted in a 48 percent reduction in lesion healing time. The severity of the herpes lesions was also reduced by use of the drug. While these results were obtained under experimental conditions, the authors believe that evaluation of higher dosages for treatment of herpes labialis may be warranted, with either oral or topical therapy.