Shire P.L.C., the world's No. 1 maker of attention deficit-disorder medications based partly in Wayne, said today it will swallow its longtime partner in ADHD drugs in a deal valued at $2.6 billion.

Shares in New River Pharmaceuticals Inc., of Radford, Va., rose nearly 9 percent in early trading to just below the per-share purchase price. Shares in U.K.-based Shire rose 4 percent.

Under the deal, which requires shareholder approval, Shire would pay $64 for each New River share, or nearly 10 percent higher than its Friday close of $58.28. Shire said it will fund the transaction with $2.3 billion in new debt and $800 million equity financing.

The deal would give Shire full control over New River's yet-unapproved drug Vyvanse, for treatment of ADHD in children. Shire and New River already have been collaborating for two years on the drug. Shire has said it expects to file by June for FDA approval.

The acquisition also would give Shire control of New River's experimental pain-reliever NRP290, now in Phase-2 trials.

Shire said it expects its tender offer to close in April 2007. New River's chief executive, R. J. Kirk, who owns 50.2 percent of the outstanding shares, has agreed to tender his shares as part of the deal.

In a statement, Shire chief executive officer, Matthew Emmens, said he sees Vyvanse as a possible successor to its current No. 1 selling ADHD medication, Adderall XR.

"This acquisition continues our leadership position in the growing U.S. ADHD market, improves our operating margins, significantly enhances our earnings growth from late 2009 and delivers on our overall global growth strategy," Emmens said.

A new product would also help Shire protect its dominance in the ADHD market from generic-drug makers which have been nipping at its revenues on Adderall. It noted that Vyvanse has "robust intellectual property with patent protection to June 2023 in the U.S. and to June 2024 in Europe."

The U.S. market for ADHD drugs was worth an estimated $3.3 billion last year, almost half of which went for drugs made by companies in the Philadelphia region, including Shire and McNeil Consumer and Special Pharmaceuticals, a Johnson & Johnson subsidiary in Fort Washington.

The deal is the second major move for relatively small Shire. In 2005, Emmens led Shire in buying the biotech firm Transkaryotic Therapies Inc. for $1.6 billion.

Shire, based in Basingstoke, about 50 miles west of London in Hampshire County, has about 2,500 employees worldwide and 600 in Wayne, where it has been building up its headquarters functions.

Contact staff writer Thomas Ginsberg at 215-854-4177 or tginsberg@phillynews.com.