Different Dosage Regimens of Methocarbamol/Paracetamol in Acute Non-specific Low Back Pain. MioPain Study

Inclusion Criteria: -Male and female patients of any ethnic origin between 18 and 64 years of age (limits included). -Patients with current episode of acute (pain lasting less than 6 weeks) non-specific LBP, defined as pain and discomfort, localised below the costal margin and above the inferior gluteal folds, with or without leg pain, or acute exacerbation of chronic low back pain defined with a VAS score ≥ 40 mm. * Patients with signs and symptoms of muscle spasm of the lumbar region, as clinically diagnosed by the Investigator. * Women of childbearing potential and women with no menses for a period \< 12 months must have a negative pregnancy test at Visit 0 and have to agree not to start a pregnancy from the signature of the informed consent up to the Final Visit/Visit 2, using an appropriate birth control method such as combined oestrogen-progestin containing hormonal contraceptives (e.g., oral, injectable, transdermal), progestin-only hormonal contraceptives (e.g., oral, injectable, implantable), intrauterine device (IUD) or Intrauterine hormone-releasing System (IUS) in combination with male condom, bilateral tubal occlusion, vasectomised partner, sexual abstinence. The following definitions will be considered: * Woman of childbearing potential (WOCBP): i.e., fertile, following menarche and until becoming post-menopausal, unless permanently sterile. Permanent sterilization methods include hysterectomy, bilateral salpingectomy and bilateral oophorectomy. * A postmenopausal state is defined as no menses for 12 months without an alternative medical cause. * Patients legally capable of giving their consent to participate in the study and available to sign and date the written Informed Consent. Exclusion Criteria: -1. Known hypersensitivity or allergy to the active ingredients and/or to any component of the study medications. 2\. Lactating and pregnant women. 3. Clinically significant abnormalities on physical examination and vital signs at Visit 0 which in the opinion of the Investigator could interfere with the study procedures or endpoints evaluation. 4\. Suspicious (according to the patient's symptoms at baseline) or confirmed COVID-19 infection at time of screening visit. 5\. History of cervical, thoracic, or lumbosacral pain for ≥75% of the time in the last year, or any other LBP episode in the last 3 months that required pharmacological treatment with an opioid analgesic. 6\. Patients with: * serious spinal pathology; spinal surgery in the year prior to screening or history of more than one spinal surgery; history of severe lumbar spinal stenosis; ankylosing spondylitis; lumbosciatalgia; herniated disc or radiculopathy; severe arthritis and osteoporosis; muscular diseases, such as myositis, poliomyelitis, muscular dystrophy and myotonia; fibromyalgia; myasthenia grave; fracture or recent history of violent trauma of the back; structural deformity of the back; * cancer, not in remission or in complete remission less than 1 year; * active influenza or other viral syndrome; immunosuppression; systematically unwell; unexplained significant weight loss; * women with polymenorrhea, endometriosis, ovarian cysts, uterine fibroids; * widespread neurological symptoms (including cauda equina syndrome) or any brain disease; ever suffered from any brain damage or have been in a coma; epilepsy or seizures; * active or suspected esophageal, gastric, pyloric channel, or duodenal ulceration, or bleeding in the last 30 days; * previous treatment with anticoagulants in the seven days before the screening visit; * renal and/or hepatic failure; * acute hepatitis; * cardiac or pulmonary diseases; * acetylsalicylic acid-triggered asthma; * glucose-6-phosphate dehydrogenase-deficient patients; glutathione deficiency, dehydration, chronic malnutrition; anemia. Any other condition that, in the opinion of the Investigator, interferes with the study endpoints/procedures and does not justify the inclusion of the patient in the study. 7\. Current use of full, regular, recommended doses of any skeletal muscle relaxants/non - opioid analgesics/anti-inflammatory/NSAIDs in the 6 hours prior to the screening visit. Use is forbidden for the entire trial duration. 8\. Current use of full, regular, recommended doses of or any medication that can alter the perception of pain (e.g., opioids, heparinoids, psychotropic agents, anti-H1 agents or glucocorticosteroids, etc.), in the 24 hours prior to the screening visit. Use is forbidden for the entire trial duration. Chronic intake of low doses of acetylsalicylic acid, i.e., ≤162 mg/daily, taken for at least 30 days prior to the first dose of study medication for non-analgesic reasons could be continued for the duration of the study. 9\. Current use of the following medications (use is forbidden for the entire trial duration): • systemic corticosteroids; * other drugs containing paracetamol; * central nervous system (CNS) depressants and stimulants, including barbiturates, anaesthetics, appetite suppressants, anticonvulsants and lamotrigine (with the exception of therapeutic doses of benzodiazepines used as hypnoinducers in patients stabilised for more than one month since the screening visit); * anticholinergic drugs; psychotropic drugs; anti-cholinesterase drugs, pyridostigmine; * oral anticoagulants; * chloramphenicol; rifampicin; zidovudine; * loop diuretics; * isoniazid; probenecid; * propranolol; * antiemetics; * metoclopramide; domperidone; * ion exchange resins (e.g. cholestyramine). 10\. Patients undergoing physiotherapy, osteopathy or chiropractic treatments aimed to reduce LBP. 11\. Patients treated with invasive procedures aimed to reduce LBP (e.g., epidural injections, spinal cord stimulation therapy). 12\. History of alcoholic/substance abuse. Use of alcohol is forbidden during the entire duration of the study. 13\. Inability to comply with the protocol requirements, instructions or study-related restrictions (i.e., uncooperative attitude, inability to return for study visits, unlikelihood of completing the clinical study); vulnerable patients (i.e., persons kept in detention). 14\. Patients involved in the conduct of the study (i.e., Investigator or his/her deputy, first grade relatives, pharmacist, assistant or other personnel). 15\. Participation to an interventional clinical trial within 3 months prior to Visit 0.