BUZZ-Valeant Pharmaceuticals: CEO Pearson to step down
** Canadian drugmaker's U.S. shares up 5 pct at $28.20
** Says CEO Michael Pearson to step down, appoints activist investor William Ackman to board
** Says started a search for a successor to Pearson
** Ackman, whose firm Pershing Square has a 9 pct stake in Valeant, will join Pershing Square's Vice Chairman, Stephen Fraidin, on the board
** "We are committed to filing the 10-K on or before April 29, 2016," Pearson said
** Up to Friday's close, stock had fallen 23 pct this year
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