Optimal timing of letermovir prophylaxis after allogeneic hematopoietic stem cell transplantation: insights from a real-world time-varying exposure analysis

Letermovir (LTV) prophylaxis effectively prevents cytomegalovirus (CMV) reactivation after allogeneic hematopoietic stem cell transplantation (allo-HSCT) [ 1 ], yet breakthrough or rebound infection often occurs after discontinuation at day 100 [ 2 , 3 ]. Although extending prophylaxis to 200 days has proven effective in randomized trials, it may increase drug acquisition costs and may postpone CMV-specific immune reconstitution during on-treatment follow-up [ 4 ]. The optimal timing for initiating and discontinuing LTV in real-world practice remains uncertain.