U.S. stocks swung between gains and losses as Merck & Co. led drugmakers lower after sales trailed forecasts and investors awaited tomorrow’s employment report to gauge the outlook for the economy. A report tomorrow may show that employment grew by 145,000 after rising by 200,000 in December, according to the median forecast of economists. The jobless rate may have held at an almost three-year low of 8.5 percent. Earlier today, Labor Department figures showed applications for unemployment insurance payments dropped by 12,000 to 367,000 in the week ended Jan. 28.

Merck lost 1.2 percent to $38.15. Revenue rose 1.7 percent to $12.3 billion, less than the analyst estimates of $12.5 billion.

Abercrombie & Fitch tumbled 12 percent to $41.31. The teen apparel chain reported preliminary fourth-quarter earnings that trailed analysts’ estimates as holiday promotions narrowed profit margins.

Citigroup rose 1.3 percent to $31.99. Morgan Stanley advanced 0.8 percent to $19.54.

Gap rallied 9.3 percent, the biggest gain in the S&P 500, to $21.27. The company forecast fourth-quarter earnings to be at least 41 cents a share, exceeding the 35-cent estimate by analysts on average.

Green Mountain Coffee Roasters Inc. surged 22 percent to $65.19. The maker of Keurig brand single-cup pods and brewers reported profit that beat analysts’ estimates as sales rose.