Merck's letermovir aces bone marrow transplant study, cutting death rate

Merck will move ahead with regulatory filings for letermovir in both the U.S. and EU this year.

Merck & Co.'s fast-tracked antiviral letermovir hit its main target of reducing infections in a trial involving bone marrow transplant patients and topped that by also reducing patient deaths.

Armed with the new data the drugmaker said it intends to move ahead with regulatory filings for letermovir in both the U.S. and EU in 2017, providing the first alternative to the current crop of generic drugs that are underused in these patients because they either lack efficacy or have toxicity issues.

The phase 3 test looked at how well letermovir was able to prevent cytomegalovirus (CMV) infections in adults undergoing a bone marrow or hematopoietic stem cell transplant (HSCT), a procedure typically used for patients with serious hematological cancers. All patients were seropositive for the virus, meaning they had been exposed to it before but had no active infection.

CMV is a common virus and usually causes no harm, but when immunity is lowered as in HSCT, it can cause serious complications including organ damage and failure. Some patients carry CMV before transplant, while in others the virus hitches a ride with the transplanted cells.

The results showed that 37.5% of patients treated with letermovir developed CMV by week 24, compared to 60.6% for a matched placebo group. And Merck's drug also led to lower all-cause mortality at 24 weeks, at 9.8% compared to 15.9% for placebo, which, as lead investigator Francisco Marty, M.D., of the Dana-Farber Cancer Institute told OncLive, was "very compelling and interesting."

The positive effect of letermovir on mortality ties in with findings from a study by Fred Hutchinson Cancer Research Center scientists last year that HSCT patients who develop high levels of CMV and other viruses in the blood post-transplant have a significantly higher mortality rate.

Letermovir could grow quickly to reach $370 million in sales by 2020, according to Credit Suisse analysts, although the drug could see a rival in the shape of Chimerix's brincidofovir, which is being tested not only for prevention of CMV but also other opportunistic infections that can affect HSCT patients.

Oral brincidofovir flopped in two phase 3 trials, but the company is pressing ahead with the development of an intravenous formulation that it hopes will protect against not only CMV but also adenovirus, another major cause of death in HSCT patients, and other DNA viruses.

The result is a welcome boost for Merck's antiviral unit after the company's $2.9 billion write-down of hepatitis C virus candidate uprifosbuvir last week in the face of a declining eligible patient population and a more difficult pricing environment for HCV drugs.

There was also good news for the Big Pharma ahead of the weekend when its shingles vaccine V212 successfully passed a first phase 3 test, preventing infections in immunocompromised patients.