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** Embattled Canadian drugmaker's U.S.-listed shares fall as much as 10.6 pct to touch near 6-year low of $23.55
** William Doyle, a key figure in Pershing Square Capital Management's controversial investment in Valeant, is leaving the hedge fund, its founder, William Ackman, told investors on Wednesday
** Valeant, which is under scrutiny from Congress, prosecutors and regulators over its drug pricing and accounting practices, appointed Joseph Papa as CEO earlier this year; Papa left Perrigo Plc in early May to replace Michael Pearson
** In a post-earnings call on Thursday, new Perrigo chief John Hendrickson criticized Papa, saying "our recent track record of performance against our own expectations is unacceptable"
** Up to Wednesday's close, Valeant's U.S shares had fallen 74 pct this year