Inveresk, a drug research firm based in Cary, has agreed to be acquired by Charles River Laboratories in a deal worth more than $1.5 billion.

Inveresk shareholders will get $15.15 in cash plus 0.48 shares of Charles River stock for a value of $38.61 per share or a total value of $1.5 billion, the company said.

Charles River stock closed at $48.87 on Wednesday.

The board of directors of the two companies announced the acquisition early Thursday morning.

Inveresk was a Scottish company when it acquired Cary-based ClinTrials in April of 2001 for $115 million. Inveresk later transferred the corporation to Delaware and went public in 2002 at $13 a share.

Under terms of the agreement, senior executives in both firms retain their jobs. Charles River did state it expected $10 million in savings from merged operations but made no mention of job layoffs or reductions. The combined operation will have 7,300 employees in 20 countries.

The company will be maintaining its headquarters in Wilmington, MA.

The deal will provide Inveresk with 27 percent ownership in the merged company.

Inveresk (Nasdaq: IRGI) and Charles River Laboratories (NYSE: CRL) said the combined company would produce “high-end products and services from discovery through the clinic.” The combined company will have more than $900 million in revenues based on figures reported through March of this year.

Inveresk stock closed at $30.84 on Wednesday, down 19 cents. It’s just off a 52-week high of $32.42. The stock was trading at under $16 last August and has risen steadily since then.

In its most recent quarterly earnings report, Inveresk reported net revenues of $12.8 million, or 31 cents per share.

“Inveresk has delivered excellent returns for shareholders by building an industry-leading services offering focused on meeting the needs of our clients,” said Walter Nimmo, chairman and CEO of Inveresk, in a statement. “The combination of Inveresk and Charles River will expand the services both companies can offer to our clients, increase opportunities for our employees and continue to deliver excellent value to our shareholders.”

Nimmo will become vice chairman and chief scientific officer of Charles River.

James Foster of Charles River remains chairman, president and CEO.
“All senior divisional operating executives of both companies will remain with the company,” the companies added.

The revamped board of directors will grow to 12 people, and Inveresk will have three seats.

“Joining our two companies is a transformational combination that builds a broader strategic platform for growth,” Foster said. “The new Charles River will be well positioned to provide essential products and services spanning the drug research and development effort, from early discovery through clinical trials. The merger will enhance our ability to serve our customers and accelerate their research efforts, while improving our operating efficiency. The combination expands our customer base and better positions us to benefit from the continuing growth in research and development spending.”