Letermovir Treatment for Refractory or Resistant Cytomegalovirus Infection

The trial will evaluate the safety and efficacy of letermovir antiviral treatment of active cytomegalovirus infection or cytomegalovirus disease in patients with infections that are refractory or resistant to available treatments or who are experiencing organ dysfunction that makes unsafe the use of available antiviral treatments.

This is a Phase II clinical trial. Phase II clinical trials test the safety and effectiveness of an investigational drug to learn whether the drug works in treating a specific disease. "Investigational" means that the drug is being studied. The FDA (the U.S. Food and Drug Administration) has not approved letermovir for treatment of cytomegalovirus infection, but it has approved letermovir for the prevention of cytomegalovirus infection in bone-marrow transplantation patients. This is the first time that letermovir will be administered to children in a clinical trial. Cytomegalovirus (CMV) is a common virus, which a majority of people acquire at some time in their life. CMV remains in your body, but does not cause symptoms in the majority of people. Patients with a weakened immune system (a system that protects you from infections) may be more at risk for the virus becoming active and causing damage to some of your organs, especially in the gut and lungs. If the virus becomes present above a certain quantity, the doctor usually prescribes a drug to treat the infection at this stage to avoid damage to the organs. In this case, the virus is no longer responding to the prescribed drug, and other drug options will be harmful to the participant's health. Participants are being invited to take part in a research study for an investigational drug called letermovir. The purpose of this study is to find out whether letermovir is as effective and as safe in treating CMV infection in patients who cannot tolerate standard treatments such as ganciclovir or foscarnet.