As the billionaire William Ackman spent four hours Friday defending his outsize bet on Valeant Pharmaceuticals International Inc., the rest of Wall Street dismissed his arguments and kept unloading shares of the besieged drug giant.

With new questions surfacing about the drug company’s business practices, Ackman, the chief executive of Pershing Square Capital Management, offered a full-throated, and at times rambling, defense of Valeant, saying its stock would bounce back and eventually reach new heights -- all the way to $448 by 2018.

In a call that sought to variously blame bad public relations, the market’s inability to understand the complexities of Valeant’s business model, jealous rivals and bad journalism, Ackman -- whose hedge fund is one of the company’s major shareholders and has been stung by the plunge in the stock -- failed to win over investors. The stock dropped to around $100 by the time the call ended and kept sinking afterward. It was trading below $94 at 3 p.m. in New York, a decline of 16 percent on the day.

"Ackman cannot know what Valeant is really doing and this call proved that," said Bill Kavaler, a New York-based managing director at brokerage firm Olivetree Financial. "There is nothing he said that isn’t already known." 

The overall picture that Ackman, and his coterie of legal and financial advisers, sought to paint was one of a misunderstood and occasionally bumbling, but essentially decent business. He dedicated little time to exploring the question of Valeant’s relationship with Philidor, the pharmacy at the center of the recent scandal rocking Valeant’s shares, and instead lashed out at what he characterized as an inept public and investor relations effort by Valeant. Particular criticism was leveled at a Valeant PR adviser, who Ackman described as having done a "horrible job."

He also blamed rival drug makers for stirring the pot when it came to Valeant’s reputation, suggesting envy at Valeant’s success had contributed to the company being cast in a negative light during recent weeks. "There are a lot of people in the pharma sector who don’t like" Valeant CEO Mike Pearson, Ackman said. That’s "because it is embarrassing for him to have twice the operating margins they do. So there is a lot of whispering."

Valeant, a Wall Street darling for years, traded over $260 back in August and was hovering at $146 last week, when the short seller Andrew Left questioned the company’s accounting practices. Left took another poke at Valeant and Ackman while he spoke today, saying that the drug maker was more likely than Herbalife Ltd. -- a stock Ackman has been betting against for years -- to fall to a stock price of zero. The comments deepened the stock’s declines.

Ackman sought to discredit Left’s claims that Valeant could be a modern-day Enron Corp. He repeatedly drew comparisons between the drug maker and Berkshire Hathaway, the acquisitive holding company of storied investor Warren Buffett. His efforts to link the two companies became so frequent that one person who dialed into the call said Ackman was trying to wrap "himself up in Buffett’s clothes." Valeant, while cutting ties today with Philidor, has denied Left’s claims that its accounting is fraudulent.

Today’s conference call, even by Ackman’s standards, was long. He started speaking at around 9 a.m. in New York, a half hour before the opening of the stock market. A steady stream of digressions left listeners confused about what exactly he was trying to achieve. There were frequent references to the room being too cold and comments on oil drilling, chess and the media’s dislike of hedge funds. There was even an, apparently unscripted, reference to JPMorgan Chase’s Jamie Dimon, upon whom Ackman bestowed the title of "the best person in the world." It was 1 p.m. by the time he finished, and the stock was showing no signs of turning around.