Pain is defined by the International Association for the Study of Pain (IASP) as 'An unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage'. Pain can be defined as either 'acute' or 'chronic'. Acute pain is generally self-limiting and has a typical duration of days to weeks, whereas chronic pain tends not to be self-limiting and can last for years.

Acute Pain

Nociceptive or acute pain is caused by transient stimulation of peripheral nerves (a.k.a., nociceptors) in response to actual or potential damage to the associated tissue. The most common causes of nociceptive pain are tissue injury (e.g., broken bone, skin laceration) or surgery. Aspirin and acetaminophen have long been used as either over-the-counter (OTC) or prescription strength treatments for mild to moderate acute pain. While their exact mechanism of action is unknown, their efficacy and tolerably are well established. OTC or prescription strength nonsteroidal anti-inflammatory drugs (NSAIDs) are also a common treatment for moderate, acute pain. This drug class includes traditional drugs such as ibuprofen and naproxen, as well as COX-2 inhibitors. While commonly used, NSAID's and COX-2 inhibitors are often associated with gastrointestinal and other significant side effects that limit their use.

Moderate to severe pain, often associated with surgery or orthopedic injury, is treated by stronger prescription strength medications, including various forms of opioid analgesics. These drug classes include short-acting generic versions of hydrocodone, oxycodone, and morphine, as well as branded longer acting patch and delayed release formulations.

Chronic Pain

Worldwide, millions of people suffer from chronic pain, including neuropathic, such as that caused by diabetes or herpes infections, and inflammatory pain, such as that caused by arthritis. In a recent European survey, the average time people experienced their chronic pain was 7 years, while many respondents reported being in pain for 20 years.

In both acute and chronic pain current treatments are burdened with side effects and offer limited efficacy. Despite recent advances in the pain field, a clear need exists for new therapeutics to combat chronic neuropathic and inflammatory pain, two particularly debilitating forms of pain.