The source did not clarify whether the CEO would be temporary or would permanently replace Pearson, 56, who is recovering from a severe case of pneumonia. Pearson’s hospitalization, disclosed on Dec. 25, is the latest challenge for the Canadian drugmaker whose shares have fallen nearly 60 percent since late August in the face of questions from Congress, investors and customers about how it prices and sells drugs. Valeant only last week said a group of company executives would take over for Pearson until he returned, an unusual arrangement that sent shares diving.