LAUSR

TO THE EDITOR—Cytomegalovirus (CMV) infection remains a frequent cause of morbidity and mortality among stem-cell and solid organ transplant recipients, with devastating complications including graft failure and death [1, 2]. Limitations of existing anti-CMV agents such as valganciclovir, ganciclovir, foscarnet, and cidofovir include toxicity (bone marrow suppression, renal failure, electrolyte disturbances), route of administration, and potential for resistance [1, 2]. Maribavir is an oral benzimidazole nucleoside inhibiting viral kinase UL97 that was Food and Drug Administration– approved in November 2021 for refractory/resistant posttransplant CMV infection [3]. In the SOLSTICE phase 3 trial of maribavir compared to investigator-assigned therapy, maribavir demonstrated superior viral clearance at week 8 (55.7% vs 23.9%, P< .0001) and fewer side effects such as neutropenia (9.4% vs 22.4%) and kidney injury (8.5% vs 9.5%) [4]. However, recurrence after treatment discontinuation occurred in 50% of initial responders [3, 4]. Additionally, treatment-emergent UL97 mutations conferring reduced maribavir susceptibility, including some conferring cross-resistance to ganciclovir/valganciclovir, occurred frequently (up to 25% of enrolled subjects) in both SOLSTICE and prior phase 2 studies [3–7]. Outside of clinical trial settings, little is known about outcomes of maribavir therapy. Here, we present 2 transplant recipients receiving maribavir who developed breakthrough CMV infection, including 1 with resistance.