Joseph C. Papa has assumed the role of chairman and chief executive officer of Valeant Pharmaceuticals International. He succeeds J. Michael Pearson. Howard B. Schiller had been appointed interim chief executive officer in January during Mr. Pearson’s medical leave of absence.   “I am thrilled to begin working closely with the talented employees across Valeant as we begin an important new chapter,” said Mr. Papa. “We have a lot of work to do, but I am confident we will succe...