Novartis AG has promoted two senior U.S. executives to head its U.S. drugs unit and overall U.S. operations. Ludwig Hantson, head of Novartis’ specialty medicines unit in the U.S., has been promoted to chief executive of Novartis Pharmaceuticals Corp., the company’s North American drugs affiliate. He succeeds Alex Gorsky, who in February resigned to become chairman of the Ethicon surgical products division of Johnson & Johnson.     Mr. Hantson has previously run Novartis&#821...