Letermovir Dosing for CMV Prophylaxis in Allogeneic HSCT Recipients

Standard Dosing Algorithm

The National Comprehensive Cancer Network recommends administering letermovir 480 mg once daily for CMV prophylaxis in adult CMV-seropositive allogeneic HSCT recipients without cyclosporine co-administration 1, 2
The National Comprehensive Cancer Network recommends reducing the letermovir dose to 240 mg once daily when co-administered with cyclosporine due to drug-drug interactions that significantly increase letermovir exposure 1, 2, 3

The National Comprehensive Cancer Network suggests starting letermovir any time between day 0 through day 28 post-transplant 1, 2
The National Comprehensive Cancer Network recommends continuing letermovir through week 14 (approximately day 100) post-transplant 1, 2
Consider extending prophylaxis through week 28 (approximately day 200) in high-risk patients, particularly those with ongoing immunosuppression or GVHD 3

Letermovir lacks activity against HSV and VZV, so concurrent acyclovir or valacyclovir prophylaxis must be continued throughout the letermovir treatment period 3, 4
Rapid emergence of resistant mutants can occur if letermovir is interrupted, underdosed, or in patients with other risk factors 1, 2, 3
The phase III trial demonstrated that letermovir 480 mg daily (240 mg with cyclosporine) through week 14 reduced clinically significant CMV infection from 60.6% with placebo to 37.5% with letermovir (P<0.001) 1, 2

The NCCN guidelines note that letermovir inhibits the CMV terminase complex, providing a novel antiviral mechanism distinct from polymerase inhibitors such as ganciclovir. 5

In the pivotal phase III randomized trial cited by the NCCN, letermovir reduced the incidence of clinically significant CMV infection from 61 % with placebo to 38 % (P < 0.001), demonstrating high‑level (Level A) efficacy for prophylaxis. 5
Observational data referenced by the NCCN indicate that, despite routine CMV surveillance, 50–60 % of CMV‑seropositive HSCT recipients experience CMV reactivation, underscoring the need for effective prophylaxis. 5

The NCCN reports that letermovir shows a superior toxicity profile: no nephrotoxicity or myelosuppression has been observed in clinical studies, contrasting with the neutropenia/thrombocytopenia of ganciclovir and the nephrotoxicity of foscarnet. 5

According to NCCN guidance, resistance to letermovir can emerge rapidly if therapy is interrupted, under‑dosed, or administered to patients with additional risk factors, making strict adherence and appropriate dose adjustment (especially when co‑administered with cyclosporine) essential. 5