Diclofenac topical formulation

1. A topical formulation comprising:

diclofenac sodium present at 2% w/w;

DMSO present at about 40 to about 50% w/w;

ethanol present at 23-29% w/w;

propylene glycol present at 10-12% w/w;

hydroxypropyl cellulose; and

water to make 100% w/w,

wherein the formulation has a viscosity of 500-5000 centipoise.

2. The topical formulation of claim 1 , wherein the formulation has a pH of 6 to 10.

3. The topical formulation of claim 1 , wherein the propylene glycol is present at 11.2% w/w.

4. The topical formulation of claim 1 , wherein the topical formulation produces less than 0.1% impurity A after 6 months at 25° C. and 60% humidity.

5. A method for treating pain due to osteoarthritis of a knee of a patient in need thereof, said method comprising:

administering to the knee a topical formulation of claim 1 ,

wherein the administration of the formulation is twice daily.

6. The method of claim 5 , wherein 2 mL of said topical formulation is administered to the knee twice daily.

7. The method of claim 5 , wherein the amount of diclofenac sodium administered to the knee is 40 mg twice daily.

8. The topical formulation of claim 1 , wherein the DMSO is present at 45.5% w/w.

9. The topical formulation of claim 8 , wherein the hydroxypropyl cellulose is present at 2.5% w/w.

10. The topical formulation of claim 1 , wherein the hydroxypropyl cellulose is present at 2.5% w/w.

11. A method for treating pain due to osteoarthritis of a knee of a patient in need thereof, said method comprising:

administering to the knee a topical formulation of claim 8 ,

wherein the administration of the formulation is twice daily.

12. A method for treating pain due to osteoarthritis of a knee of a patient in need thereof, said method comprising:

administering to the knee a topical formulation of claim 9 ,

wherein the administration of the formulation is twice daily.