Shares of Merck & Co. were headed higher in early Thursday trading, after the drugmaker extended its long streak of quarterly earnings beats and held firm with its full-year outlook despite expected tariff costs.Shares of Merck & Co. were headed higher in early Thursday trading, after the drugmaker extended its long streak of quarterly earnings beats and held firm with its full-year outlook despite expected tariff costs. Shares of Merck & Co. were headed higher in early Thursday trading, after the drugmaker extended its long streak of quarterly earnings beats and held firm with its full-year outlook despite expected tariff costs.   Read More MarketWatch.com – Top Stories