Virologic Characterization of Multidrug-Resistant Cytomegalovirus Infection in 2 Transplant Recipients Treated with Maribavir

The experimental cytomegalovirus UL97 kinase inhibitor maribavir was used to treat 2 cases of infection in which viral mutations that conferred ganciclovir and foscarnet resistance had evolved sequentially. In one case, viral shedding was cleared without evidence of maribavir resistance in an isolate obtained after therapy. In the other case, a high-grade viremia was initially reduced 50-fold but rebounded 2 months later, coincident with the emergence of viral UL97 mutations T409M and H411Y, which confer maribavir resistance. The relatively rapid onset of maribavir resistance probably resulted from incomplete viral suppression in an immunosuppressed host with a high viral load.