Once-daily intravenous acyclovir for prophylaxis of herpes simplex virus reactivation after marrow transplantation.

To determine the most convenient and least expensive regimen for prevention of recurrent herpes simplex virus (HSV) infection after marrow transplantation, we conducted a randomized, double-blind comparison of intravenous acyclovir 250 mg/m2 and placebo given once daily for four weeks. Six of 14 acyclovir and nine of 13 placebo recipients shed HSV during prophylaxis. All nine culture-positive placebo recipients developed associated lesions during prophylaxis compared to four of six acyclovir recipients. Median time to first culture-positive lesion was significantly delayed by acyclovir compared to placebo (33 days after transplant vs. 10; P = 0.05). Acyclovir-resistant HSV was recovered from one acyclovir recipient while receiving prophylactic acyclovir, and from two placebo recipients during subsequent administration of therapeutic acyclovir. Once-daily intravenous acyclovir can significantly delay time to appearance of culture-positive HSV lesions after marrow transplant, but virological and clinical breakthrough may occur and optimal prevention will require administration of intravenous acyclovir more than once daily.