Tuesday, September 30, 2014

Dissolution study of polylactic acid based in situ gels

Dissolution study of polylactic acid based in situ gels [prolonged release for 12 days]

In situ gel delivery systems become viscous when the solution is immersed in dissolution medium (or body fluid) at body temperature. The gel may take very long time to get completely dissolved, thus slowly releasing the drug.


USP Dissolution rate test apparatus, graduated pipette (2ml cap.), phosphate buffer solution (pH 7.4), sodium azide, 


  • Gel formulation of 10 ml is taken in a small porcelain or glass cup and placed at the bottom of  a USP-2 dissolution rate test apparatus (paddle type). The round bottom jar is filled with 900ml phosphate buffer (pH7.4). Temperature is maintained at 370C. 
  • For a prolong released product the time of dissolution may require 12 days or more. In such case, to prevent bacterial growth, sodium azide (final concentration in the 900 ml dissolution medium 0.02%w/v  ) is used.
  • The paddle speed is fixed at 50 rpm. Sample (1ml) is collected from the dissolution medium at 1, 3, 6, 9, 12 days interval. After each sampling the round bottom beaker is replenished with 1ml of fresh dissolution medium pre-warmed at 370C.
  • The samples are filtered by centrifugation and finally analyzed with HPLC.


Xin, C., Lihong, W., Qiuyuan, L., Hongzhuo, L., 2014. Injectable long-term control-released in situ gels of hydrochloric thiothixene for the treatment of schizophrenia: Preparation, in vitro and in vivo evaluation. International Journal of Pharmaceutics 469, 23–30.

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