Efficacy and Safety of Etoricoxib/Tizanidine Versus Etoricoxib for Acute Low Back Pain Associated to Muscle Spasm

Inclusion Criteria: * Willing to participate in the study and provide written informed consent. * Diagnosis of acute low back pain, either as a first-time episode or following a previous episode within the past 6 months, with a duration not exceeding 6 weeks. * Pain associated with lumbar muscle spasm, assessed through physical examination (muscle hypertonia and/or reflex scoliosis) and clinical history. * Patient reports moderate to severe pain intensity (VAS ≥ 40 mm). * Patients with a Neuropathic Pain Questionnaire (DN4) score \< 4. * For women of childbearing age who are sexually active, the use of an acceptable contraceptive method (barrier and/or hormonal) as determined by the investigator. * At the discretion of the Principal Investigator (PI) or treating physician, the patient is eligible for treatment with the investigational product and may benefit from it. Exclusion Criteria: * Patients with a history of hypersensitivity to any components of the investigational product (Etoricoxib/Tizanidine) or their derivatives (as reported in the medical history and clinical interview). * Patients participating in another clinical trial involving an investigational treatment or who have participated in one within the past 2 weeks before the study begins. * Patients whose participation in the study may be influenced (e.g., employment relationship with the research center or sponsor, vulnerable populations, etc.). * Patients for whom the investigational drug is contraindicated …