Safety and Efficacy Study of an Etoricoxib and Tizanidine Fixed Dose Combination in Participants With Moderate to Severe Acute Low Back Pain (MK-0663B-164)

Inclusion Criteria: * Have acute low back pain; * Onset of acute low back pain must be \<6 weeks prior to screening; * Have acute low back pain corresponding to a rating of ≥ 4 on a 0-10 point Low Back Pain Questionnaire and ≥ 7 on the Roland Morris Questionnaire; * For women of childbearing potential, have a negative serum pregnancy test at Visit 1 (Screening Visit) and agree to remain abstinent, use barrier, or non-hormonal implanted contraceptives from study start until 14 days after the last dose of study drug; * Be willing to limit alcohol use, if any, to 2 drinks or equivalent per day for the duration of the study and follow-up period; * Be willing to avoid unaccustomed physical activity (e.g., starting a new weight lifting routine) for the duration of the study and follow-up period; * Be willing to avoid chiropractic care, ultrasound and physical therapy from screening to Day 9; * Be willing to avoid cold applications and other alternate treatments (e.g. massage, acupuncture etc.) on Day 1 and within 30 minutes prior to scheduled pain assessments on Day 3 and Day 8. Exclusion Criteria: * Has low back pain that is related to, or known to be caused by malignancy, inflammatory disease (rheumatoid arthritis, ankylosing spondylitis, psoriatic arthritis, Reiter's syndrome), osteoporosis, ochronosis, vertebral fracture, infection, juvenile scoliosis, congenital malformation, or fibromyalgia. Note: the presence of radiographic degenerative disc disease is not an exclusion; …