Efficacy and Safety of Fixed-dose Combination of Etoricoxib/Tramadol vs Acetaminophen/Tramadol for Acute Low Back Pain

Inclusion Criteria: * Any sex. * That the subject agree to participate in the study and give informed consent in writing. * Age\> 18 years and ≤ 60 years of age at the beginning of the study. * Diagnosis of acute low back pain as a first-time episode or after another episode, maximum 6 months before and lasting no more than 6 weeks. * Patient with low back pain reported as moderate to severe intensity (VAS\> 4 cm). * Women of childbearing age who have an acceptable contraceptive method (eg barrier, oral hormonal, injectable, subdermal). Exclusion Criteria: * Patients in whom the study drug is contraindicated for medical reasons. * Patients with an allergy or hypersensitivity to the active principle, study drugs, related products or excipients. * Positive pregnancy test, women who are pregnant, breastfeeding or planning a pregnancy while conducting the study. * A significant history of gastrointestinal disorders (for example: Gastric ulcer, Crohn's disease, Ulcerative Colitis, etc.). * Previous treatment with opioids and / or NSAIDs (Non-Steroidal Anti-Inflammatory Drugs) reported in the medical history in the last 72 hours at study entry. * Patients with a history of alcohol or drug abuse in the last year according to DSM-V (Diagnostic and Statistical Manual of Mental Disorders). * Patients who are receiving monoamine oxidase inhibitors (MAOIs) or who have received them within the past 2 weeks. * Patients with a history of established ischemic heart disease, peripheral arterial disease and / or cerebrovascular disease (including patients who have recently undergone coronary artery bypass grafting or angioplasty). * Patients with status epileptic seizure disorders and grand mal seizures. * Patients with a history of severe acute or chronic liver failure. * Patients with a history of moderate to severe renal failure. * Patient with a history of chronic pain (eg, fibromyalgia, Paget's disease, bone pain induced by metastatic cancer). * Low back pain due to major trauma (eg vertebral fracture, post-traumatic spondylolisthesis), or due to a visceral disorder (eg dysmenorrhea, endometriosis). * At medical criteria, a disease that affects the prognosis and prevents outpatient management, for example, but not restricted to: intestinal obstruction, paralytic ileus, end-stage cancer, kidney, heart, respiratory or liver failure or mental illness or with surgical procedures or scheduled hospitals. * History / presence of any disease or condition that, in the Investigator's opinion, could pose a risk to the patient or confuse the efficacy and safety of the study results. ----Patients with symptoms suggesting an active COVID-19 infection (i.e., fever, cough, dyspnea) and / or contact in the past 14 days with a suspected or positive COVID-19 patient. * Oncological patients (except basal cell skin cancer) or with serious diseases that, in the opinion of the investigator, have a serious prognosis or a life expectancy of less than 1 year, as well as mental illnesses. * The patient is participating in another clinical study involving an investigational treatment or participated in one in the previous 4 weeks. * Patients whose participation in the study may be influenced (employment relationship with the research center or sponsor, inmates, etc.).