Study to Assess the Efficacy and Safety of Tizaspray® Versus Sirdalud®, in Patients With Acute Low Back Pain

Inclusion Criteria: 1. Age between 18 and 65 years old 2. Average low back pain intensity moderate to severe (≥ 60 mm in the VAS) at Visit 1 3. Positivity to Schober test (i.e. measure \< 5 cm) at Visit 1 4. Acute low back pain started at least 24 hours prior to inclusion in the trial and more than 6 weeks after the last episode of acute low back pain 5. Negative pregnancy test for women of childbearing potential (to be performed at Visit 1) and use of an acceptable mean of contraception (condom or mechanical methods) in the previous 2 months and for whole duration of the study 6. Signed Informed Consent Exclusion Criteria: 1. History of chronic low back pain 2. Current treatment with drugs having significant effects at the alpha2 receptors whether agonist (i.e., clonidine, methyldopa) or antagonist (i.e., phenothiazines, imipramine) 3. Current treatment with any other muscle relaxant or any drugs having muscle relaxant properties 4. Known allergies, hypersensitivity, or intolerance to tizanidine or paracetamol or any excipients used in their manufacture (included patients with known rare hereditary problems of galactose intolerance, the Lapp lactase deficiency or glucose-galactose malabsorption) 5. Signs of nasal congestion, nasal polyps, mucosal lesions of the nostrils, postnasal drip of any etiology or any clinically significant nasal pathology that may affect the absorption of study medication or the assessment of safety 6. Evidence of clinically unstable disease, as determined by medical history, physical examination, that, in the Investigator's opinion, preclude entry into the study 7. Spinal surgery within 1 year of study entry 8. Evidence of clinical gastrointestinal malabsorption 9. Use of steroids within 3 months of study entry or any other long-term treatment with steroids 10. Use of NSAID's or other anti-inflammatory drugs 6 hours prior to study inclusion 11. Use of fluvoxamine or ciprofloxacin, or other inhibitors of CYP1A2 such as antiarrhythmics (amiodarone, mexiletine, propafenone), cimetidine, fluoroquinolones (enoxacin, pefloxacin, norfloxacin), rofecoxib, oral contraceptives, and ticlopidine 12. Use of hypnotics or other CNS depressants 13. Blood pressure \<100/70 mmHg 14. History of lumbar spinal stenosis, fibromyalgia, or ankylosing spondylitis 15. Severe scoliosis 16. More severe pain in a region other than the lower back 17. Acute low back pain associated with chills or fever 18. Pregnancy, breast feeding 19. Treatment with another investigational agent within the last 30 days 20. Known or suspected history of alcohol or drug abuse based on medical history, physical examination, or the Investigator's clinical judgment