After hep C hit, Merck's antiviral business nabs approval for CMV fighter Prevymis

Merck & Co.'s antiviral business suffered some serious blows this year, but it now boasts a brand-new drug: Prevymis, a cytomegalovirus fighter now FDA-approved to prevent infection in adults undergoing stem cell transplants.

Those patients are at particular risk of any sort of infection, and though CMV is harmless to most people, it can be deadly to patients who've received bone marrow transplants. Given for up to 100 days after a transplant, Prevymis is designed to fend off infection and prevent reactivation in patients who already carry the virus.

Analysts have said the drug, cleared by the FDA on Thursday, could quickly build to sales of $370 million by 2020. That is just about 1% of Merck's annual pharma revenue, but at a time when the company is facing eroding Remicade sales in Europe and new generic competition to its cholesterol drugs Zetia and Vytorin, every few hundred million helps.

Plus, it's some welcome good news for the anti-infectives business, which took a $2.9 billion writedown on one hepatitis C med early this year and canned its three-drug hep C combo in September. Merck had spent $3.9 billion to buy Idenix and its hepatitis C meds back in 2014.

Merck expects to launch Prevymis in December at a list price of $195 per day for the tablet version and $270 per day for the injectable. At the maximum 100 days of treatment, that's $19,500, or $27,000 per treatment course, before payer discounts and rebates. 

The approval is based on a phase 3 trial showing that 38% of patients treated with Prevymis (letermovir) developed CMV by week 24, compared to 61% for a matched placebo group. Merck's drug also led to lower all-cause mortality at 24 weeks, at 9.8% compared to 15.9% for placebo. Prevymis' positive effect on mortality rate echoed previous findings from a study by Fred Hutchinson Cancer Research Center scientists, who found that patients who develop high blood levels of CMV and other viruses after a stem cell transplant are significantly more likely to die.

"Our findings demonstrate that letermovir is a significant and welcomed advance in the prevention of clinically significant CMV infection and lowers mortality in this highly vulnerable patient population," said Francisco M. Marty, M.D., associate professor of medicine at Harvard Medical School and the Merck study's lead author, in the approval release.

It's the first new medicine for CMV infection approved in the U.S. in 15 years, Merck noted in its statement. The FDA approval triggers a $105 million milestone payment to AiCuris, which licensed the drug to Merck in 2012.