By Kristina Cooke and Ransdell Pierson

NEW YORK (Reuters) - The chief executive of drugmaker Bristol-Myers Squibb Co (BMY.N: Quote, Profile, Research) bought 100,000 company shares in his first open-market purchase since taking the top post nearly two years ago, according to a regulatory filing on Thursday.

James Cornelius purchased $2.3 million worth of stock on Wednesday for $22.70 to $22.92 a share, according to a U.S. Securities and Exchange Commission filing.

On the same day, the drugmaker said it was evaluating its 2008 earnings forecast and would update its full-year outlook by the end of the second quarter. For details, see [nWNAS2439]

Cornelius, who became chief executive in 2006, is the first insider to directly buy on the open market since at least February 2001, according to insider filing tracker InsiderScore.com.

Bristol-Myers Squibb shares, which were little changed at $22.81 on Thursday, are down 14.3 percent year-to-date.

The chief executive of rival Schering-Plough Corp (SGP.N: Quote, Profile, Research), Fred Hassan, bought about $2 million of his company's common stock, or 110,000 shares, two weeks ago, keeping an earlier pledge to make the personal investment as a vote of confidence in the struggling drugmaker.

Hassan announced his plans to buy the stock on Jan. 18, after a failed clinical trial of the company's big-selling Vytorin cholesterol drug spurred a 20 percent decline in the shares that week.

The financial picture of New York-based Bristol-Myers has greatly improved in recent quarters, following the brief U.S. appearance of a generic form of its blockbuster blood clot preventer, Plavix, that badly hurt the branded drug.