Merck’s Antiviral Drug Meets Primary Endpoint in Phase III Clinical Trial

Merck’s investigational antiviral medicine, letermovir, has met its primary endpoint of reducing the incidence of cytomegalovirus (CMV) infection in adults following a bone marrow transplant. In addition, patients in the Phase III clinical trial who were given the antiviral prophylactically, showed a lower mortality rate after the procedure.

“These results showed that letermovir prophylaxis beginning after hematopoietic stem cell transplant (HSCT) and continuing through Day 100 post-transplant significantly reduced CMV infection requiring preemptive antiviral therapy through Week 24 post-transplant,” said Dr. Francisco M. 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. “In this study, letermovir was associated with lower all-cause mortality. 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.”

This latest data was presented on Sunday at the BMT Tandem Meetings – the combined annual meetings of the Center for International Blood & Marrow Transplant Research (CIBMTR) and the American Society for Blood and Marrow Transplantation (ASBMT). According to Merck, they intend to apply for approval of letermovir in the US and the EU this year.

CMV is a common virus which is normally asymptomatic in healthy individuals. However, when a patient is immunosuppressed – as is the case for patients following a bone marrow transplant as treatment for hematological cancers – CMV can cause serious complications, including organ damage and failure.

All patients in the Phase III clinical trial had previously been exposed to CMV, but were not suffering from an active infection at the time of the study. While generic antiviral drugs are available to reduce the risk of infection following an HSCT, they are largely underused due to issues of safety and efficacy.

The results of the study showed that 37.5 percent of patients treated with letermovir developed a CMV infection by the 24-week post-HSCT mark, compared to 60.6 percent for the placebo. Letermovir was also associated with lower all-cause mortality, with 9.8 percent of patients given the antiviral dying before week 24, compared to 15.9 percent for the placebo.

“There is an unmet need for therapeutic options in the prevention of CMV infection in hematopoietic stem cell transplant recipients,” said Dr. Nicholas Kartsonis, vice president, infectious disease clinical research, Merck Research Laboratories. “As part of Merck’s long-standing commitment to developing innovative approaches in the fight against infectious diseases, we look forward to submitting regulatory applications for letermovir this year.”

According to FierceBiotech, Credit Suisse analysts have predicted that letermovir could see sales of $370 million by the year 2020, if approved by regulators. Despite its potential, letermovir shows no activity against other viruses, making it vulnerable to competition from more broad-spectrum antivirals, like Chimerix’ brincidofovir.