Merck said it no longer plans to seek regulatory approval for the drug in the United States and is recommending that providers not start new patients on it.

The failed study had enrolled more than 25,000 patients over more than three years and is a significant setback for the drugmaker because Tredaptive was one of the most important and potentially lucrative of its experimental medicines.

Merck shares were down almost 3 percent at $42.35 compared to Wednesday's closing on the New York Stock Exchange.

(Reporting By Caroline Humer and Ransdell Pierson)