Factors affecting solubility and stability of indomethacin in mixed micelles

The solubility and stability of indomethacin in bile salt/phosphatidylcholi n-mixed micelles (BS/PC-MM) were investigated as function of some formulati on parameters. The solubility of indomethacin is greatly influenced by pH, buffer concentration, and temperature, as well as by composition of MM, At the same pH, the solubility of indomethacin in MM is highly enhanced compar ed with that in buffer only. Moreover, the solubilizing capacity has been s hown to be strongly dependent on the micellar system as compared with other surfactants. The solubility profile deviated from linearity at increasing micellar concentration due to the gradual drop in pH by solubilized indomet hacin, The stability study indicated apparent first order degradation kinet ics either in buffer or in MM with substantial increase in stability in MM, The degradation constant showed exponential dependence on the pH of the di spersion medium. An Arrhenius plot could be constructed from which a shelf stability of more than 1.5 years was obtained in sodium glycocholate/soya p hosphatidylcholine-mixed micelles (SGC/SPC-MM) at 25 degrees C.