The plunge in Valeant Pharmaceutical International Inc.'s stock on Monday could be costing billionaire investor William Ackman over $600 million in one day. Ackman's hedge fund, Pershing Square Capital Management, owned 19.5 million shares, or 5.7%, of Valeant's shares outstanding as of June 30, according to FactSet. That makes Valeant the largest holding of Pershing Square, and makes Pershing the third-largest sharedholder in Valeant. The stock tumbled $31.18, or 16%, in afternoon trade, following reports that House Democrats were seeking a subpoena to force Valeant to turn over documents related to massive drug price increases. If Ackman still owned the 19.5 million shares he owned at the end of June, those shares would be worth about $607.2 million less than they were on Friday. Since biotechnology stocks turned sharply lower a week ago, after presidential candidate Hillary Clinton said she'd lay out a plan to prevent price gouging by drugmakers, Valeant's stock has lost $73.85, or 30%, meaning Ackman would have lost $1.44 billion.
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