The purpose of this study is to determine if two sustained released formulations of carisoprodol are more effective than placebo.

Methodology:

This will be a randomized, double-blind, double-dummy, placebo-controlled, parallel-group study in subjects 18-70 years of age with acute, painful, muscle spasm of the lower back. The study consists of a baseline screening (Study Day 1), during which subjects will be evaluated for inclusion/exclusion criteria, and a 7-day double-blind treatment period (Study Day 1 through Study Day 7). Subjects will be randomly assigned to be dosed twice daily with one of the following double-blind treatments: SR carisoprodol 500-mg tablets, SR carisoprodol 700-mg tablets, or placebo.

Subjects will be evaluated in the clinic on Study Days 1, 3 and 7. Subjects who remain symptomatic on Study Day 7 will be allowed to continue in the study for a 7-day, double-blind extension period at the discretion of the Investigator. Subjects will be contacted by telephone for a safety follow-up 7 days after the last dose of study medication.

A pharmacokinetic (PK) substudy will be conducted at selected sites. These sites will obtain blood samples for PK analysis at the end of the 7-day treatment period and the 14-day treatment period, if applicable.

Inclusion Criteria:

• Onset of pain is within 3 days of first visit
• Subject rating of pain must be 40 mm or greater on VAS
• Ability to discontinue all analgesics, NSAIDs, and other muscle relaxants
• Willingness to provide written informed consent
• Must be in generally good health

Exclusion Criteria:

• Presence of sciatic pain
• History of clinically significant spine pathology such as herniated nucleus pulpous, spondylolisthesis, spinal stenosis
• Presence of underlying chronic back pain
• Neurological signs and symptoms such as numbness, tingling, foot drop, paresthesia, unexplained constipation, urinary retention or urinary incontinence
• Myocardial infarction within one year of study
• Cancer not in remission or in remission less than one year
• HIV or other immunodeficiency syndromes
• History of osteoporosis or at high risk for vertebral fracture
• Underlying rheumatologic disease such as rheumatoid arthritis, ankylosing spondylitis, etc.
• Presence of active influenza or other viral syndromes
• Morbid obesity (BMI >39)
• Evidence of infection, such as low grade fever or neutrophilia
• Existence of any medical/surgical condition that could interfere with the evaluation of the study medication
• Known history of alcohol or drug abuse
• Injury involving high potential for litigation, including worker's compensation or automobile accidents
• Pregnancy or breast feeding
• Women of child-bearing potential not abstinent or not practicing a medically acceptable method of contraception
• Vertebral body or spinous process, percussive tenderness on physical exam
• Any abnormalities in the following tests of both lower extremities: ankle dorsiflexion strength, great toe dorsiflexion strength, absent or hyperreflexic Achilles or patellar tendor reflexes, abnormal sensory exam in the medial, dorsal or lateral aspect of the foot and positive straight leg raise test
• Urgent medical conditions on comprehensive exam that might indicate a more serious condition should be treated urgently