RADFORD - New River Pharmaceuticals Inc. announced a drug-development agreement that positions the small Radford company to share in the U.S. profits from its planned treatment for attention-deficit hyperactivity disorder and collect up to $500 million from partner Shire Pharmaceuticals Group plc.

The two companies said Monday they will collaborate to develop, manufacture, market and sell a drug New River invented in its laboratory at the Virginia Tech Corporate Research Center and which is in the midst of human testing. The Food and Drug Administration has yet to approve the drug. The agreement represents a milestone for New River Pharmaceuticals, a specialty pharmaceutical company that has been in the discovery and development phase for eight years and operates with money invested by private and public shareholders.

"We are delighted to announce this agreement with Shire, a company that we believe will bring substantial value to this project," said R.J. Kirk, chairman and chief executive of New River Pharmaceuticals, in a prepared statement.

Kirk said Shire is an ideal partner because of its experience in the field of central nervous system drugs. Shire sells the leading product on the market for ADHD, Adderall XR.

New River's drug, known in the laboratory as NRP104, "is a strong addition to our ADHD portfolio," said Matthew Emmens, chief executive officer of Shire, in a prepared statement. "We are encouraged by the data that we have seen to date and hope that the new drug has similar efficacy of currently marketed ADHD treatments with potential additional advantages. Importantly, NRP104 could become a global product."

The drug is a stimulant, a compound proven to help patients improve their focus. But New River Pharmaceuticals said its version also incorporates proprietary technology designed to make it less abusable. Abuse of prescription stimulants for attention-related disorders is a recognized and growing problem, federal officials say.

The announcement doesn't say how much it will cost to bring the drug to market, but explains that New River Pharmaceuticals will pay to complete tests on people and lay the groundwork for manufacturing. Shire will head up sales, but New River Pharmaceuticals will also play a role in sales.

Shire will book the sales and keep 75 percent of operating profits earned in the United States for two years, giving New River Pharmaceuticals the rest. After two years, the companies plan to split the operating profits, they said.

The agreement calls for Shire to pay New River Pharmaceuticals $50 million at signing, $50 million more if and when the application for approval from the FDA is accepted and up to $300 million more depending on unspecified elements of the label the FDA approves. Shire also agreed to pay New River Pharmaceuticals an additional $100 million if the product sells well.

Shire received a license to develop and commercialize the drug outside the United States. It will pay New River Pharmaceuticals a "low double-digit royalty" on those sales, the companies said.

Shares of New River Pharmaceuticals, traded on the Nasdaq under the symbol NRPH, closed Monday at $23.95, up $1.45. Shire's American stock, which trades as SHPGY, closed unchanged at $35.