Merck & Co said it is planning to submit regulatory applications for letermovir in the US and European Union sometime this year, on the back of late-stage data showing its promise in preventing a serious viral infection in patients undergoing a bone marrow transplant.

The firm, which is known as MSD outside the US and Canada, is developing the antiviral for the prevention of clinically-significant cytomegalovirus (CMV) infection in adult CMV-seropositive recipients of an allogeneic haematopoietic stem cell transplant (HSCT).

Top-line data from a pivotal Phase III trial of the drug show that significantly fewer patients with undetectable CMV DNA at the start of study treatment developed clinically significant CMV infection through Week 24 post-HSCT: 37 percent in the letermovir arm versus 60.6 percent in the placebo group.

In addition, letermovir prophylaxis was associated with lower all-cause mortality through Week 24 post-HSCT (9.8 percent versus 15.9 percent for placebo), Merck said.

"Based on these findings, letermovir as primary prophylaxis of CMV infection represents a potential new strategy for the prevention of CMV in this high-risk patient population," noted Dr Francisco Marty, associate professor of medicine at Harvard Medical School and attending physician in transplant and oncology infectious diseases at Dana-Farber Cancer Institute and Brigham and Women's Hospital, presenting the data at the recent BMT Tandem Meetings in Orlando, Florida.

Letermovir has been granted orphan designation by the European Medicines Agency, the US Food and Drug Administration and the Japanese Ministry of Health, Labour and Welfare for the prevention of CMV infection and disease in at-risk populations.