Oral valacyclovir as prophylaxis against herpes simplex virus reactivation during high dose chemotherapy for leukemia

Reactivation of herpes simplex virus is a common event in patients undergoing dose-intensive remission induction or consolidation chemotherapy of acute leukemia, for which either intravenous or oral acyclovir provides effective prophylaxis. This drug's short serum half-life and low oral bioavailability make frequent dosing necessary, however, and we therefore sought to determine if the pro-drug valacyclovir, which has improved bioavailability, could be successfully substituted for this indication. Eighty-one patients with leukemia were randomized to receive either 500 mg or 1,000 mg of valacyclovir orally every 8 h and followed clinically, as well as with serial surveillance cultures. Over a total of 1,979 days on study between the groups, and 380 throat cultures, no documented episodes of herpes simplex reactivation were noted. Valacyclovir was tolerated well with no evident drug-related toxicities. We conclude that valacyclovir at either of the two doses studied can be safely substituted for oral or intravenous acyclovir, and that it provides effective prophylaxis against reactivation of herpes simplex virus in this patient population.