Impax Pharmaceuticals, Hayward, Calif, has initiated a Phase IIb trial of its drug candidate IPX159 in patients with moderate to severe restless legs syndrome (RLS).

The Phase IIb study is a multicenter, randomized, double-blind, placebo-controlled, safety and efficacy study to evaluate IPX159. The trial is expected to randomize approximately 120 adults who will receive either IPX159 or placebo and will be treated for up to 11 weeks. The trial will be conducted at multiple sites in North America. The primary endpoint is the International Restless Legs Syndrome Study Group (IRLSSG) Rating Scale.

The company plans to report results of the study and provide an update on the program in mid-2013.