Shares of Merck and Amgen Inc. are trading lower Tuesday morning, sending the Dow Jones Industrial Average into negative territory. The Dow DJIA, -0.76% was most recently trading 210 points lower (-0.6%), as shares of Merck MRK, -2.39% and Amgen Inc. AMGN, -2.71% are contributing to the blue-chip gauge’s intraday decline. Merck’s shares have declined $1.77 (2.3%) while those of Amgen Inc. have dropped $5.17, or 2.3%, combining for a roughly 46-point drag on the Dow. Also contributing significantly to the decline are 3M MMM, -3.02%, Boeing BA, -2.32%, and Travelers TRV, -1.24%. A $1 move in any one of the 30 components of the index equates to a 6.58-point swing.