AD 337 is the active single isomer of a racemic drug that is currently marketed for a different indication. It is a serotonin noradrenaline reuptake inhibitor which Sosei R&D Ltd. intends to develop as an oral product to treat fibromyalgia syndrome (FMS). FMS is an under-diagnosed disorder of unknown etiology affecting an estimated 2-4% of the general population, of which approximately 80% are women. Patients complain that they ache all over and a large number of other symptoms are often present, particularly fatigue, morning stiffness, sleep disturbance and headaches. Positive results in pain models demonstrated that AD 337 may be particularly effective for this indication and a Phase I single and multidose studies that it is well tolerated and has an attractive pharmacokinetic profile. However, results of Phase II proof of principle study completed in September 2007 showed that a significant outcome was not achieved in the primary endpoint, although statistical significance was achieved at earlier time points and positive trends were seen throughout the study.