U.S. stocks fell in choppy trade and the Nasdaq closed at its lowest level since October 2002 on Monday as shares of the biggest drugmakers fell after Merck's proposed $41 billion takeover of Schering-Plough .

* The Dow Jones industrial average <.DJI> fell 79.89 points, or 1.21 percent, to end unofficially at 6,547.05. The Standard & Poor's 500 Index <.SPX> lost 6.85 points, or 1.00 percent, to 676.53. The Nasdaq Composite Index <.IXIC> shed 25.21 points, or 1.95 percent, to 1,268.64.

(Reporting by Leah Schnurr; Editing by Jan Paschal)