Tolerability, Safety and Activity of a Muscle Relaxant Molecule IDN5243 in Patients With Low Back Pain

Inclusion Criteria: * Male or female patients, * 18-70 years old inclusive, * Signed Informed consent obtained prior the inclusion in the trial, * A diagnosis of LBP equal to or greater than 50 mm on VAS with severe or moderate lumbar muscle spasm naïve or in relapsing condition, * Patients must have a medical history, physical and neurological examinations that support a clinical diagnosis of acute LBP that is felt down to the lower leg below the knee with the onset no longer than 30 days before Visit 1, * Patients must be appropriate candidates for treatment with study medication in the Investigator's clinical judgment, * Patients must be able to appropriately verbalize pain characteristics and to complete all protocol required measurements/assessments without assistance, * Patients must be medically stable on the basis of physical examination, medical history, vital signs, and clinical laboratory tests performed at screening. Exclusion Criteria: * LPB of non-mechanical origin such as neoplasm, infection or inflammatory chronic disorder, * Serum creatinine level \> 1.7 mg/dL or Urea \> 17 mmol/l, * Severe to mild hepatic dysfunction, * Abnormal blood count, * Ascertained or presumptive hypersensitivity to the active principle and/or formulations' ingredients, * History of anaphylaxis to drugs or allergic reactions in particular, history of hypersensitivity reactions (e.g. bronchospasm, rhinitis, urticaria) to drugs including to paracetamol, * Patients with diabetic neuropathy, post-herpetic neuralgia, osteoarthritis pain, fibromyalgia, * History of psychosis (e.g. schizophrenia or psychotic depression) or major depression (requiring treatment), diagnosis including dementia, anxiety, mental retardation; multiple sclerosis, Parkinson's Disease, Restless Legs Syndrome, * Significant kidney or liver disease, * History of gastrointestinal disorders, * Blood coagulation disorders, * Skin conditions affecting the site of application (e.g. eczema, weeping dermatitis), * Use of paracetamol and/or NSAIDs (NonSteroidal AntiInflammatory Drugs) within 24 h before inclusion, * Use of topical medications applied to the painful region within 2 days before the inclusion; use of opioids within 7 days before the inclusion, * Use of corticosteroid drugs by any route of administration within 30 days before the inclusion, * Use of myorelaxant drugs within 3 days before the inclusion, * Pregnant or lactating women, or women of childbearing age not using a reliable method of contraception, or women of not child-bearing potential if not permanently sterilised or if not in post-menopausal status from at least two years, * Males not to agree to use a reliable method of contraception during the study and the follow up period, if sexually active with a female of child-bearing potential, * History of back (cervical, thoracic or lumbosacral) pain as 50% of the time in the 1 year prior to the first visit, * History of any LBP episode, with the exception of the current acute LBP episode, within 3 months prior to the first visit that was greater than mild in pain intensity, or was associated with disability (e.g., loss of time from work, family, or activities of daily living), or necessitated the use of an opioid (narcotic) analgesic including tramadol, * Medical history or physical examination results that suggest the acute LBP or any of the neurological symptoms or signs are caused by a serious medical condition (e.g., fever, chills, unexplained weight loss, bowel or urinary bladder dysfunction or incontinence, bilateral leg weakness, progressive weakness, paralysis), * There is a high probability for surgical intervention for the back pain during the projected time on the study or that there will be an increase in the severity of the leg pain or deficits, * Had either a surgical procedure involving the spine or intervertebral discs in the lower back region within 1 year prior to Visit 1 or had \>1 surgical procedure(s) involving the spine or intervertebral discs in the lower back region, * Has any painful condition that could interfere with the study assessments or with the patient's ability to differentiate the pain associated with the acute LBP episode from pain associated with another condition, * History of epilepsy or recurrent seizures, * Unable or unwilling to discontinue all prohibited medications at the time of randomization and during the time of their participation in the study, * Known or suspected history of alcohol or drug abuse based on medical history, physical examination, urine drug screening, or the Investigator's clinical judgment, * Have filed or plan to file a worker's compensation claim for any issue related to the current acute LBP episode, * Currently involved in litigation or plan to seek legal recourse for any issue related to their acute LBP, * Known allergies, hypersensitivity, or intolerance to the study drug or any excipients used in their manufacture, * Had previously been enrolled in a muscle relaxant clinical study within 30 days before the inclusion.