GlaxoSmithKline ($GSK) is punting on Horizant. The U.K.-based drugmaker is kicking the restless legs syndrome drug back to partner XenoPort after a series of setbacks, including disappointing sales and a partnership dispute. Horizant hasn't performed up to either company's expectations. Its road to FDA approval was long and hard, but it finally won the agency's blessing last April. Sales didn't exactly skyrocket on launch, and XenoPort blamed Glaxo for the lackluster performance. In fact, after XenoPort posted just $1.3 million in first-quarter net sales, the smaller company tried to formally terminate the marketing agreement. Article