The primary objective of this study is to evaluate the efficacy of a 14-day dosing regimen of ATB-346 at doses of 150 mg, 200 mg and 250 mg compared to placebo in reducing osteoarthritis knee pain as measured by changes in the post-treatment WOMAC subscale pain score relative to each patient's pretreatment baseline WOMAC assessment.Safety will be assessed via measurements of vital signs and clinical laboratory tests at baseline and at various time points during the study, patient monitoring, and by the documentation of adverse events.

The primary objective of this study is to evaluate the efficacy of a 14-day dosing regimen of once daily administration of ATB-346 at doses of 150 mg, 200 mg and 250 mg compared to placebo in reducing osteoarthritis knee pain as measured by changes in the post-treatment WOMAC subscale pain score relative to each patient's pretreatment baseline WOMAC assessment.A total of 360 evaluable patients are planned in this study: 250 mg (n=120); 200 mg (n=120); 150 mg (n=60); placebo (n=60).

Safety will be assessed via measurements of vital signs and clinical laboratory tests at baseline and at various time points during the study, patient monitoring, and by the documentation of adverse events.

Inclusion Criteria:

• Diagnosis greater than 2 years duration requiring the use of regular therapies, e.g. oral or topical anti-inflammatories, acetaminophen, topical capsaicin
• Between the ages of 40 to 75
• BMI ≤40
• Patients must be unlikely to procreate or agree to the use of acceptable contraceptive regimens from first drug administration , during the study, and for at least 30 days after the last dose
• Patients must not have used aspirin or naproxen-containing medications for 7 days prior to study entry
• Patients must not have used any anti-inflammatory medications or acetaminophen for 5 days prior to study entry
• Patients must show a ≥10-point increase in WOMAC Visual Analog Score between their screening visit and baseline study entry visit

Exclusion Criteria:

• Females who are pregnant or breastfeeding
• Seated and resting pulse rate less than 50 beats per minute (bpm) or more than 100 bpm at screening
• Seated and resting blood pressure below 100/60 mmHg or higher than 140/90 mmHg at screening
• History of significant hypersensitivity to naproxen, other non-steroidal anti-inflammatory agents, or any related products (including excipients of the formulations) as well as severe hypersensitivity reactions (like angioedema) to any drugs
• Patients with a history of GI bleeding or ulceration
• Patients refractory to NSAIDs
• Presence of significant gastrointestinal, liver, or kidney disease, or any other conditions known to interfere with the absorption, distribution, metabolism or excretion of drugs or know to potentiate or predispose patients to undesired effects
• Presence of significant cardiovascular, pulmonary, hematologic, neurological, psychiatric, endocrine, immunologic, or dermatologic disease as determined by the investigator
• Suicidal tendency, history of/or disposition to seizures, state of confusion
• History of hepatic disease
• Maintenance therapy with any drug, including gastroprotective agents such as proton pump inhibitors, H2 receptor antagonists, sucralfate, etc., or significant history of drug dependency or alcohol abuse (>3 units of alcohol per day, intake of excessive alcohol, acute or chronic)
• Any clinically significant illness in the previous 30 days before Day 1 of this study
• Use of any enzyme-modifying drugs, including strong inhibitors of CYP enzymes (such as cimetidine, fluoxetine, quinidine, erythromycin, ciprofloxacin, fluconazole, ketoconazole, diltiazem, and HIV antivirals) and strong inducers of CYP enzymes (such as barbiturates, carbamazepine, glucocorticoids, phenytoin, rifampin and St John's Wort) in the previous 30 days before Day 1 of this study
• Any history of tuberculosis and/or prophylaxis for tuberculosis
• Positive H. Pylori Urea Breathe Test
• Positive urine screening of alcohol and/or drugs of abuse at the screening visit
• Positive results to HIV Ag/Ab Combo, Hepatitis B surface Antigen (HBsAg) or anti-Hepatitis C Virus (HCV) tests
• Females who are pregnant according to a positive serum pregnancy test
• Patients who took an Investigational Product (in another clinical trial) in the previous 30 days before Day 1 of this study.

Overencapsulation of study drug tablets