Aqueous suspension preparation for injection, method for producing the same and use thereof for producing pain relief

A process for producing an aqueous suspension preparation for injection to combat pain comprising a water-insoluble local anesthetic and/or narcotic analgesic in the form of particles wherein more than 99% of said particles have a diameter of less than 100 .mu.m and more than 90% have a diameter of less than 50 .mu.m, the mean particle diameter being less than 20 .mu.m, said particles being suspended in an aqueous medium wherein the sole agent for stabilizing the suspension is a non-ionic surface-active agent in an amount of less than 1 wt. %, said process comprising:

• suspending the water-insoluble local anesthetic in powder form in the aqueous medium containing the non-ionic surface-active agent to form a suspension;
• sterilizing the suspension thus obtained at about 120 deg. C. for about 20 minutes to form a wholly liquid mixture;
• cooling the wholly liquid mixture to room temperature while vigorously stirring or shaking said liquid mixture;
• then freezing the cooled liquid mixture at a temperature between 0 deg. C. and -25 deg. C. to form a frozen mixture;
• and
• defrosting the frozen mixture while vigorously shaking the frozen mixture.