US-based pharmaceutical firm Merck has enrolled the first patient in a global Phase III clinical trial of letermovir (MK-8228), an investigational antiviral agent, for prevention of cytomegalovirus (CMV) infection in high-risk bone marrow transplant patients.

The trial will assess the efficacy and safety of letermovir for the prevention of clinically-significant CMV infection in adults aged 18 years and older CMV-seropositive recipients of allogeneic hematopoietic stem cell transplants.

Letermovir is being developed for the prevention of human CMV infection and has secured orphan product designation from the European Medicines Agency (EMA) and the US Food and Drug Administration (FDA) for the prevention of CMV viremia.

Merck Research Laboratories Infectious Diseases executive director Michele Trucksis said: "There remains a need for additional therapeutic options in the prevention of CMV infection in high-risk patients.

"Merck is pleased to initiate this global Phase III study with letermovir."

In 2012, Merck through a subsidiary purchased worldwide rights to develop and commercialise letermovir from AiCuris.

AiCuris CEO Helga Rübsamen-Schaeff said: "This study marks a very important step in the development of letermovir and for AiCuris as licensor of this compound."

"In 2012, Merck through a subsidiary purchased worldwide rights to develop and commercialise letermovir from AiCuris."

In the multicentre, randomised, placebo-controlled trial, letermovir will be administered once daily, either as an oral tablet or intravenous (IV) formulation, for 14 weeks after transplant.

Letermovir 240mg dose will be given once-daily for patients who receive concomitant cyclosporin A and 480mg once-daily for people not receiving cyclosporin A.

The primary outcome measure of the Phase III trial will be the percentage of participants with clinically-significant CMV infection through 24 weeks after transplant who were administered letermovir compared to placebo.

Approximately 540 patients at more than 70 centres in 20 countries, including the US, will be enrolled in the trial, which is scheduled to be completed in July 2017.

Image: Typical "owl eye" inclusion indicating CMV infection of a lung pneumocyte. Photo: courtesy of Angusmclellan.