A Study to Evaluate the Safety and Tolerability of Arbaclofen Placarbil (XP19986) in Subjects With Acute Back Spasms

Inclusion criteria

• Acute moderate to severe muscle spasms in the lumbar region, as indicated by a minimum Visual Analog Scale pain severity score of 4.0 cm, beginning either:

• within four days prior to screening for subjects who do not require a 24-hour washout

Or

• within three days for subjects who require a 24-hour washout
• Willing to discontinue all analgesics (e.g. NSAIDS, COX-2 inhibitors, acetaminophen), aspirin >81 mg/day, short-acting muscle relaxants (i.e. carisoprodol, Soma®), and herbal remedies for pain at least 24 hours prior to first dose and to refrain from use during the study (cardio-protective doses of aspirin ≤ 81 mg /day are allowed).

Exclusion criteria

• Clinically significant abnormal neurological history or examination at screening (excluding back spasm), including lumbar radicular symptoms, spinal stenosis, foot drop, herniated nucleus pulposus, or other structural defects
• Subjects with back spasm related to major trauma to the region
• Subjects with muscle spasms due to a work-related injury or subjects involved in any injury-related litigation
• Subjects using any of the following medications at screening:

• Opioids, both short- and long-acting including but not limited to: morphine, fentanyl patch, oxycodone, tramadol)
• benzodiazepines, such as valium and lorazepam
• cyclobenzaprine containing drugs (e.g., Flexeril, Amrix)
• carisoprodol (e.g., Soma®) within 24 hours of screening