Merck & Co. will lay off personnel by the end of October, according to a company e-mail to staff, as the pharmaceutical giant continues cutting its workforce.

The company, with about 12,000 workers in the Philadelphia area, said July 29 that it planned to cut 12 percent to 13 percent of its workforce of about 100,000 by 2015 as it adjusts to market conditions and its 2009 acquisition of Schering Plough.

"Merck is facing enormous challenges," U.S. Market president Mark Timney said in an e-mail Thursday to staff that was obtained by The Inquirer. The e-mail was first reported by the pharmaceutical blog Pharmalot. "The external environment is tougher than ever, with an unprecedented pace of change that continues to accelerate."

Company officials confirmed that Timney's e-mail was authentic but declined any other comment.

"In the coming weeks, we will restructure the following select HQ functions and field groups within the U.S. Market: Marketing & Customer Solutions; Managed Markets & Policy; Strategy & Commercial Model Innovation; and the Neuropsychiatric and Women's Healthcare specialty sales teams," Timney's e-mail said.

Merck eliminated jobs before and after its acquisition of Schering Plough.

Merck's headquarters is in Whitehouse Station, N.J., but the company has several facilities elsewhere in New Jersey and a large operation in West Point, Montgomery County.

Pharma-industry watchers have suggested that about 5,200 of the total cuts could be U.S. jobs, with from 3,000 to 4,000 in New Jersey and Pennsylvania. A Merck spokesman would not comment on the state-by-state plans. The cuts through October won't be the end of the process, though.

In August, Merck offered buyout packages to some employees, but there was no expectation that the buyouts alone would meet the numbers required by management. Merck said that in some areas it would continue to add employees but cut elsewhere.

Timney said the company was open to voluntary layoffs:

"We will also offer the opportunity for employees in the aforementioned select areas to proactively 'hand raise' and be considered for separation."