Carl Icahn accused drug maker Forest Laboratories Inc. (FRX) Chief Executive Howard Solomon of selling more than $500 million of stock ahead of the company's loss of patent exclusivity on antidepressant Lexapro, as the activist investor stepped up his attack on the drug maker's management.

The billionaire investor has been in a long-running battle with Forest Labs, a skirmish revived earlier this month when he nominated four candidates to its board and said he was seeking records of the company's actions. Icahn said last week he is suing Forest Labs in an effort to get information from the drug maker about its plans for a successor to Mr. Solomon, who is 84 years old.

"Several years ago you began a pattern of selling Forest stock at prices substantially higher than today's price. Those sales now look to me like a savvy bet against the prospects of a company that was not prepared to meet the calamitous events that would befall it .. when Lexapro went off patent," Icahn wrote in a letter released Monday.

Icahn said shareholders who "were not privy to your knowledge and still hold stock today have suffered very significant losses."

The company wasn't immediately available for comment.

Icahn, known for his battles with corporate boardrooms, is the company's second-largest shareholder, with a roughly 10% stake, according to data provided by FactSet Research.

On Friday, Icahn said in a regulatory filing that the company has "refused to provide us with documents concerning a number of items" and told the company's board that he was commencing litigation.

The company disputed Icahn's claims Friday, saying suggestions that it hasn't been transparent about plans for a successor to Solomon "could not be further from the truth."

Last August, the drug maker's shareholders rejected Icahn's effort to place four of his director nominees on the board and elected Forest's entire slate instead.

In June, Forest Laboratories reduced its fiscal-year earnings guidance because of lower-than-expected branded Lexapro sales and more aggressive pricing for the authorized generic version of the antidepressant following the March loss of the drug's patent exclusivity.

Shares were up 2% to $35.70 in recent trading. The stock has gained 18% so far this year.

Write to Kristin Jones at kristin.jones@dowjones.com

Forest Road Acquisition (NYSE:FRX)
Historical Stock Chart
From Jun 2024 to Jul 2024 Click Here for more Forest Road Acquisition Charts.
Forest Road Acquisition (NYSE:FRX)
Historical Stock Chart
From Jul 2023 to Jul 2024 Click Here for more Forest Road Acquisition Charts.