Prevention of herpes zoster in patients by long-term oral acyclovir after allogeneic bone marrow transplantation.

Following allogeneic bone marrow transplantation for leukemia, herpes zoster infections that are potentially severe with a high risk of dissemination develop in 30 to 50 percent of patients. Intravenous acyclovir is an effective treatment for established zoster in immunocompromised persons. Oral acyclovir has relatively low bioavailability, which has made the value of this route of administration for the treatment or prophylaxis of herpes zoster infections uncertain. In this trial, 82 patients undergoing allogeneic bone marrow transplantation for leukemia were randomly assigned to receive either intravenous acyclovir for 23 days followed by oral acyclovir for six months, or matched placebos; the random groups were well-matched in all clinical characteristics. During the six-month period of acyclovir/placebo administration, no patient receiving acyclovir developed herpes zoster, whereas six patients receiving placebo did so (p = 0.006). During the six-month follow-up, there were six cases of zoster in the treatment arm of the study and two cases in the placebo arm. Herpes zoster was not restricted to those patients who had positive evidence of antibody before transplant. This study shows that oral acyclovir is capable of preventing zoster infection during its period of administration; once the drug treatment is stopped, infections occur. In selected patients, the use of long-term oral acyclovir may be of value in preventing zoster infections during the time of greatest immunosuppression.