FDA approves Merck blood thinner for some patients

WASHINGTON (AP) -- The Food and Drug Administration has approved a new type of blood thinner from Merck that reduces heart attack, stroke and other fatal cardiovascular events in patients with a history of heart attack.

The approval of Zontivity marks a comeback for a drug which was once hailed as a potential blockbuster, but has been plagued by bleeding side effects in clinical testing. In 2011 Merck took a $1.7 billion charge to write down the value assigned to the tablet, after studies showed it increased the risk of internal bleeding in the skull.

But Merck successfully retooled the drug as an option for patients who have had a recent heart attack but have not had a stroke or internal bleeding. Merck had originally sought a broader market.

Zontivity, known generically as vorapaxar, is the first of a new class of drugs called protease-activated receptor-1 antagonists. The drugs work by preventing blood platelets from clumping together to form a blood clot.

Internal bleeding is a common side effect of blood thinning drugs, and Zontivity will carry a boxed warning that it can cause potentially deadly bleeding side effects. In particular, the label warns that the drug must not be used in people who have had a stroke due to the risk of intracranial bleeding.

Patients should talk to their doctor if they have unexpected, prolonged bleeding or find blood in their stool or urine, the FDA said in its announcement of the approval.

The FDA cleared the drug based on a study of over 25,000 patients in which adding Zontivity to older blood thinners reduced a combined measure of heart attack, stroke and cardiovascular death.

The new tablet enters a crowded field of new blood thinning drugs, including Boehringer Ingelheim's Pradaxa; Johnson & Johnson and Bayer Healthcare's Xarelto and Pfizer Inc. and Bristol-Myers Squibb Co.'s Eliquis.

Those drugs are already approved for a slew of uses in preventing strokes and blood clots in patients with a variety of health conditions.

Drugmakers have generally touted these therapies as more effective and safer than Coumadin, known chemically as warfarin. That's been the standard treatment for decades though it is difficult to administer because of the need for frequent blood tests to ensure it is being dosed properly.

Shares of Whitehouse Station, New Jersey-based Merck & Co. Inc. rose 6 cents to $54.83 in afterhours trading Thursday.