UPDATE 1-Schering-Plough CEO buys shares, keeps pledge

(Adds details on stock purchase, background)

NEW YORK, April 24 (Reuters) - Schering-Plough Corp (SGP.N: Quote, Profile, Research) said Chief Executive Fred Hassan bought about $2 million of the drugmaker's common stock on Thursday, keeping an earlier pledge to make the personal investment as a vote of confidence in the company.

Schering-Plough said he purchased 110,000 shares at an average price of $18.26 on the open market, where they are traded on the New York Stock Exchange.

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

At the time, the company said Hassan had hoped to buy the shares the previous day, when they closed at $21.62 on the NYSE, but would be unable to do so until the transaction received legal clearance. Permission was granted earlier on Thursday, the company said, a day after Schering-Plough reported first-quarter earnings.

"As I said when I announced my intention to purchase these shares in January, this investment in Schering-Plough reflects my long-term confidence in the company, its products -- including Zetia and Vytorin -- and our late-stage pipeline," Hassan said on Thursday in a release.

Researchers earlier in January said Vytorin failed its primary goal of reducing fatty plaque in the carotid artery more effectively than the widely used generic cholesterol fighter simvastatin, which is also the active ingredient of Merck & Co's (MRK.N: Quote, Profile, Research) Zocor.

Vytorin -- which combines Zocor with the newer cholesterol treatment Zetia -- cut levels of "bad" LDL cholesterol far better than simvastatin, but that was not the trial's main focus.

Schering-Plough sells Vytorin and Zetia through a joint venture with Merck.