Feb 10 (Reuters) - Biotech company Targacept Inc said British drugmaker AstraZeneca would return rights to several pre-clinical compounds, sending the U.S. company's shares down 10 percent in extended trading.

A licensing agreement, signed in 2005, continues for the remaining compounds, including AZD1446, a potential treatment for Alzheimer's disease.

The amendment to the agreement becomes effective 90 days after Feb. 7, Targacept said in a filing with the U.S. Securities and Exchange Commission. ()

Targacept shares closed at $4.96 on the Nasdaq on Monday.