The purpose of this study is to evaluate efficacy and safety of SI000413 in patients with knee osteoarthritis by orally administration and to determine optimal dose.

This is a dose-response, double blind , placebo-controlled study. All patients are required to have 2 weeks washout period from prior medication. Subjects will discontinue current medications 2 weeks prior to randomization. Among those who meet the inclusion criteria, only subjects recording visual analogue scale(VAS) of higher than 40mm(VAS range from 0mm(no pain) to 100mm(unbearable pain)) are enrolled in this study.

Subjects meeting screening criteria will be randomized to receive 8 weeks dosing of an active dose of SI000413 or placebo.

Inclusion Criteria:

1. Males and females, 35-75 years old

2. Subjects must have a clinical or radiographic diagnosis of primary OA of the knee (diagnosed according to the ACR)

   • The presence of knee pain

   • At least one of the following

     • age older than 50 years
     • morning stiffness lasting less than 30 minutes
     • crepitus with motion

3. Subjects must have been symptomatic for at least 3 months prior to enrollment.

4. Subjects must be required to have experienced a pain intensity of at least 40mm on a 100-mm visual analogue scale in the most severely affected joint during the 24 hours prior to randomization.

5. Adequate liver and kidney function

   • Adequate liver function : SGOT, SGPT must be within 1.5 x normal limit
   • Adequate kidney function : Serum creatinine must be within 1.5 x normal limit

6. Subjects must be able to read, understand and follow the study instructions

7. Subjects must agree to informed consent spontaneously.

Exclusion Criteria:

1. Subjects who are not using adequate birth control.
2. Pregnant or breast-feeding.
3. Subjects requiring Knee surgery within 1 year of screening anticipating any need for a surgical procedure during the study.
4. Secondary OA patients
5. Similar OA patients(ex. rheumatic arthritis, bursitis etc)
6. Treatment with intra-articular injections of systemic corticosteroids or hyaluronic acid in the prior 3 months.
7. Use of drugs or psychotropic medicine(methadone maintenance program, codeine, tramadol hydrochloride)
8. Anemia or coagulant disorder
9. Use of anticoagulants or lithium
10. Use of misoprostol or H2-blocker(including anti ulcer medicine)
11. Presence or history of gastrointestinal bleeding within the past 1 year.
12. Subjects who have serious problem with cardiovascular, respiratory, endocrine, central nervous or History of neurotic mental.
13. Active malignancy of any type(ex. lymphoma, multiple myeloma etc)
14. Use of any medication that will affect pain perception during the study period; physical therapy, corticosteroids, NSAIDs, asprin, topical analgesics.
15. Use of glucosamine, chondroitin during the study period.
16. Change of concomitant dose/use within 4 weeks.
17. Known allergy or hypersensitivity to medicine.
18. Subjects received hormone replacement therapy.
19. Use of any other investigational drug within 1 month prior to screening.
20. Investigators determines that it is not appropriate.