US STOCKS-Dow falls into negative territory, Merck drags

NEW YORK, July 9 (Reuters) - The Dow slipped into negative territory while the S&P 500 and the Nasdaq pared gains on Thursday, as drugmaker Merck (MRK.N) fell on concerns over its cholesterol drug.

* The Dow Jones industrial average .DJI dropped 7.94 points, or 0.10 percent, to 8,170.47. The Standard & Poor's 500 Index .SPX gained 1.84 points, or 0.21 percent, to 881.40. The Nasdaq Composite Index .IXIC added 6.26 points, or 0.36 percent, to 1,753.43. (Reporting by Chuck Mikolajczak; Editing by Leslie Adler)