The most common causes of chronic pain are musculoskeletal problems and inflammatory conditions. Injuries from accidents resulting in fractures, dislocations or soft tissue injury, as well as lower back pain, are the most frequent causes of musculoskeletal pain. Although these injuries are mostly non-fatal, the cost in terms of disability, medical expense and lost productivity is enormous. The inflammatory conditions of osteoarthritis and rheumatoid arthritis affect approximately 20 million Americans. Therapeutics goals in these diseases focus on reducing pain and stiffness and improving daily functionality and activity. The overall chronic pain market associated with musculoskeletal pain is expected to exceed $8 billion by 2010.

The 2005 FDA warning related to cardiovascular adverse events associated with NSAIDs has significantly altered the competitive landscape for therapeutics developed to teat chronic pain conditions.