Trial to See if Topical Pennsaid for Knee Pain Affects Coagulation Values in Patients Who Are Also Taking Anticoagulants

Inclusion Criteria: * Male or female adults \> than or equal to 55 * Ambulatory subjects with moderate to severe osteoarthritis (OA) of the knee with symptoms and knee pain for at least 3 months and pain on the majority of days in the last 30 days. * Subjects with bilateral knee OA, the more symptomatic knee is the index knee and PENNSAID can be applied on both knees if both are affected. * Radiographic evidence of Kellgren-Lawrence Grade 2-4 within the past 2 years. * Currently on a stable dose of anticoagulant therapy (warfarin, dabigatran, aspirin or clopidogrel) for the past 2 months and expected to remain on current dose for the six week duration of the study. * If currently taking oral nonsteroidal antiinflammatory drug (NSAID) and/or acetaminophen for OA knee pain, must be taking it for at least an average of 25 days per month. * Those currently taking oral NSAID must be willing to perform a 7 day washout to be eligible to be enrolled into the study. * A pain score of \> than 40mm on the Patient Pain Visual Analog Scale (VAS) (100 mm scale) at screening and baseline visit. * Able to comply with the study and give informed consent prior to performance of any study procedures. * Able to read, write and understand English. Exclusion Criteria: * Unwilling to abstain from oral NSAIDs and/or other analgesic medication except for acetaminophen as rescue medication. Subjects taking low dose aspirin for cardiovascular health may remain on their stable dose throughout the study. * Unwilling to abstain from taking \< than or equal to 1500mg of acetaminophen a day for rescue medication purposes during the 6 week course of the trial. * Using a handicap assistance device i.e. cane, walker \> than or equal to 50% of the time. * Undergoing new physical therapy or participating in a weight loss or exercise program that has not been stable for at least 3 months prior to screening and won't remain stable during participation in study. * History or diagnosis of an inflammatory arthritis i.e. rheumatoid arthritis, psoriatic arthritis, ankylosing spondylitis, arthritis associated with inflammatory bowel disease, sarcoidosis, or amyloidosis. * Known or clinically suspected infection and human immunodeficiency virus (HIV), or hepatitis C or B viruses. * History of abnormal laboratory results \> that or equal to 2.5 x upper limit of normal (ULN) indicative of any significant medical disease which in the opinion of the investigator, would preclude the subjects participation in the study. * Any of the following abnormal laboratory results during screening: * Alanine aminotransferase (ALT) and aspartate aminotransferase (AST) \> than or equal to 2.5 x ULN * Hemoglobin \< than 11.5 g/dL (female) or \< 13.2 g/dL (male) * White blood cell count (WBC) \< than 3500 cells/mm3 * Lymphocyte count \< than or equal to 1000 cels/mm3 * Serum creatinine \> than or equal 1.5 x ULN * Platelet count below the central laboratory lower limit of normal (LLN) * Coagulation tests (Prothrombin Time (PT), Partial Thromboplastin Time (PTT), International Normalized Ratio (INR), Platelet Aggregation) requiring an alteration in anticoagulant dosage. * Skin breakdown or rash at knee where topical PENNSAID is to be applied. * Other serious uncontrolled non-malignant, significant, acute or chronic medical or psychiatric illness that, in judgment of investigator, could compromise subject safety, limit subject's ability to complete study and/or compromise the objectives of study. * History of malignancy in the past 5 years with exception of resected basal cell carcinoma, squamous cell carcinoma of the skin, or resected cervical atypia or carcinoma in situ. * History of drug or alcohol dependence or abuse in the past 3 years.