It has been estimated that over 100 million patients suffer from either acute or chronic pain annually in the United States . Global pain and inflammation markets are growing at an average of 30% per year and are estimated to reach the $40 billion level by 2010. Existing pain medications, including opioid analgesics, non-steroidal anti-inflammatory drugs (NSAIDs) and selective cyclo-oxygenase inhibitors (COX inhibitors), are frequently limited by numerous adverse effects. Consequently, the pain and inflammation market represents a therapeutic area where substantial unmet patient need will drive significant market share for innovative products with reduced side effects.

The current market for analgesics is segmented by the severity of the pain. Mild-to-moderate pain is typically treated with non-steroidal anti-inflammatory drugs (NSAIDs) which are useful for this indication, but ineffective in moderate-to-severe pain. Moderate-to-severe pain, on the other hand, is treated with opioids which are effective but have a poor side effect/safety profile which prevents their use in mild-to-moderate pain indications. These DEA-scheduled drugs have many characteristics or side effects which limit their use, including:

• tolerance (loss of effectiveness over time with repeated administration)
• dependence (addiction) and risk of debilitating withdrawal syndrome
• potentially lethal respiratory depression
• nausea and vomiting
• severe, painful constipation or ileus (bowel obstruction) with complications
• drowsiness and sedation
• dysphoric reactions (restlessness, tremulousness, hyperactivity)
• urinary retention
• increased intracranial pressure
• postural hypotension
• pharmacological treatment of overdose results in withdrawal syndrome