Valeant Pharmaceuticals International Inc.'s stock was the most active trading on U.S. exchanges Tuesday, as it plunged as much as 22% intraday to the lowest level since August 2010 before recovering slightly, after the drug maker slashed its earnings outlook for the year. Volume hit 52 million shares within the first hour of the regular session, compared with the full-day average over the past 30 days of 32.7 million shares, according to FactSet. The stock has lost 16% since March 21, which is when the company announced that billionaire activist investor Bill Ackman had joined its board of directors. The latest filings indicate Ackman's hedge fund Pershing Square Capital Management owned 21.6 million Valeant shares as of March 31; with the stock down 8.2% since then, Ackman has lost nearly $47 million on his investment in a little over two months.
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