Acyclovir prophylaxis of recurrent genital herpes: randomised placebo controlled crossover study.

Forty patients were entered into a randomised placebo controlled crossover study to assess the efficacy and safety of oral acyclovir 200 mg four times a day in the prophylaxis of recurrent genital herpes. Each treatment began during a recurrence and continued for a maximum of 84 days or until the onset of the next recurrence, when the alternate medication was started. Of 28 patients who completed both treatment courses, only three developed a recurrence while taking acyclovir compared with 26 while taking placebo. The mean time to first recurrence was more than 84 days in patients receiving acyclovir and 24 days in patients receiving placebo (p less than 0.001). The mean time to first recurrence after treatment with acyclovir ceased was 16 days. Adverse events, though thought unlikely to be related to treatment, necessitated the withdrawal from the study of two patients while taking acyclovir and one patient while taking placebo. No clinically important effects on haematological or biochemical variables occurred during the acyclovir treatment. All viral isolates tested after treatment remained sensitive to acyclovir. Acyclovir prophylaxis of recurrent genital herpes is effective and safe but does not appear to influence the natural history of the disease after cessation of 84 days' continuous treatment.