One-year low-dose valacyclovir as prophylaxis for varicella zoster virus disease after allogeneic hematopoietic stem cell transplantation. A prospective study of the Japan Hematology and Oncology Clinical Study Group.

Varicella zoster virus (VZV) disease is a frequent complication after allogeneic hematopoietic stem cell transplantation (HSCT).  We carried out a trial of 1-year low-dose valacyclovir (VCV) prophylaxis against VZV disease to evaluate its efficacy and safety. Patients received oral acyclovir (ACV) 1000mg/day until day 35 after HSCT. Oral VCV 500mg/day, 3 times a week, was started on day 36 and continued until 1 year after HSCT. The development of VZV disease was monitored until 2 years after HSCT. A total of 40 patients with a median age of 43 years were enrolled. VCV was well tolerated in all but 1 patient who discontinued it on day 224 because of thrombocytopenia of unknown cause. Seven patients developed VZV disease at a median of 479 days (range 145-651) after HSCT, with a cumulative incidence of 18.5%. Two patients developed breakthrough disease during VCV prophylaxis. The other 5 patients developed VZV disease after the discontinuation of VCV, and 3 of these had developed extensive chronic graft-versus-host disease. Visceral involvement and serious complications were completely eliminated. All patients responded to the therapeutic dose of VCV or ACV. One-year low-dose VCV can be safely and effectively administered for the prevention of VZV disease after allogeneic HSCT.