Billionaire activist investor Bill Ackman, founder of Pershing Square Capital, is hosting a conference call for investors Friday morning to discuss his fund's investment in Valeant Pharmaceuticals.
The call will take place at 9 a.m. ET, with Ackman and other Pershing Square portfolio managers and analysts taking questions.
Since taking a position earlier this year, Pershing Square has likely lost more than $1.5 billionon paper on Valeant, the fund's largest stock holding.
Shares of the Canadian drug company have collapsed since Wednesday after the California-based short-selling firm Citron Research published a report asking whether Valeant was operating an Enron-like fraud.
Citron's report focuses on the company's relationship with Philidor, a specialty pharmacy that distributes prescription drugs for Valeant. Valeant is the only supplier to Philidor, and it also has an option to buy the company. On Wall Street, no one had really heard of Philidor until earlier this month.
Citron has accused Valeant of using Philidor, and an unknown number of specialty pharmacies like it, to generate fake invoices so it can book revenue for sales that never happened.
Valeant has categorically denied the allegations in the Citron report. The company hosted an all-hands call Monday morning to address the allegations.
Valeant's share price has declined by more than 40% since the report came out.
Valeant's share price was last trading at around $99.91 per share in the after-hours session Thursday after CVS and Express Scripts terminated their relationships with Philidor.

What's at stake?

Ackman's Pershing Square Capital Management owns 21,473,933 shares of Valeant, including 2 million shares Ackman bought during last Wednesday's sell-off.
Pershing Square is Valeant's third-largest shareholder. The stock is Ackman's largest investment. The losses have dragged down his fund's performance.
Pershing Square Holdings, the fund's publicly traded vehicle, is down 15.9% this year through Tuesday, October 27.
Ackman first disclosed his position in Valeant March 17, when the share price was $200 per share. At that share price, the position was worth $3.9 billion. With his added shares from last week, Ackman's position is worth $2.14 billion. That would represent a loss of around $1.76 billion.
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