Method for obtaining an injectable hydrogel based on hyaluronic acid containing lidocaine and an alkaline agent, sterilized with heat

1. A method for obtaining an injectable hydrogel comprising crosslinked hyaluronic acid, or a salt thereof, and lidocaine, the method comprising the following successive steps:

i) making a gel comprising crosslinking hyaluronic acid or one of its salts with butanediol diglycidyl ether (BDDE),

ii) adding lidocaine hydrochloride as a powder in the gel and then mixing,

iii) adjusting the pH to a value of between 6.5 and 7.6 by adding an alkaline agent to the gel and lidocaine hydrochloride mixture, and homogenizing the mixture to obtain a hydrogel which does not contain any suspended solid lidocaine particles, and

iv) sterilizing the hydrogel with heat,

wherein following the addition of the alkaline agent at step iii), a dilution percentage of the gel is less than or equal to 2.5%, and wherein the dilution percent is defined as V1*100/(V1+V2), wherein V1 is the volume of the added alkaline solution and V2 is the volume of the gel after adding lidocaine hydrochloride and before adding the alkaline solution.

2. The method of claim 1 , wherein the concentration of the hyaluronic acid or of one of its salts obtained in step i) is between 1 mg/ml and 50 mg/ml.

3. The method of claim 2 , wherein the concentration of the hyaluronic acid or of one of its salts obtained in step i) is between 4 and 40 mg/ml.

4. The method of claim 3 , wherein the concentration of the hyaluronic acid or of one of its salts obtained in step i) is between 14 and 35 mg/ml.

5. The method of claim 1 , wherein the molecular mass of the hyaluronic acid or of one of its salts is between 1,000 daltons (Da) and 10×10 6 Da.

6. The method of claim 5 , wherein the molecular mass of the hyaluronic acid or of one of its salts is between 2×10 5 Da and 5×10 6 Da.

7. The method of claim 6 , wherein the molecular mass of the hyaluronic acid or of one of its salts is between 5×10 5 Da and 4×10 6 Da.

8. The method of claim 1 , wherein the hyaluronic acid or one of its salts is crosslinked and exhibits a crosslinking degree of between 0.1% and 25%.

9. The method of claim 8 , wherein the hyaluronic acid or one of its salts is crosslinked and exhibits a crosslinking degree of between 0.5% and 15%.

10. The method of claim 9 , wherein the hyaluronic acid or one of its salts is crosslinked and exhibits a crosslinking degree of between 1.5% and 14%.

11. The method of claim 1 , wherein the lidocaine hydrochloride concentration of the gel is between 0.1 and 50 mg/ml.

12. The method of claim 11 , wherein the lidocaine hydrochloride concentration of the gel is between 1 and 30 mg/ml.

13. The method of claim 12 , wherein the lidocaine hydrochloride concentration of the gel is between 2 and 20 mg/ml.

14. The method of claim 1 , wherein the alkaline agent is selected from the group consisting of sodium bicarbonate, sodium hydroxide and potassium hydroxide.

15. The method of claim 1 , wherein the dilution percentage of the gel is less than or equal to 1.5%.

16. The method of claim 15 , wherein the dilution percentage of the gel is less than or equal to 1%.

17. The method of claim 1 , wherein the pH of the hydrogel before and after sterilization is between 6.5 and 7.6.

18. The method of claim 17 , wherein the pH of the hydrogel before and after sterilization is between 6.9 and 7.5.

19. The method of claim 18 , wherein the pH of the hydrogel before and after sterilization is between 7.0 and 7.4.

20. The method of claim 19 , wherein the pH of the hydrogel before and after sterilization is between 7.1 and 7.3.

21. The method of claim 1 , wherein the sterilization of the hydrogel is carried out in humid heat.