Solid dispersions of nimodipine and polyethylene glycol 2000: dissolution properties and physico-chemical characterisation

The incorporation of a drug in a carrier by melt embedding may either result in a solid solution or in a solid suspension of the active ingredient within the carrier material. As the dispersivity of the drug is of outstanding importance for its dissolution characteristics, parameters which are supposed to influence crystallinity and dispersivity, e.g. cooling rate during preparation and storage conditions like temperature and relative humidity are investigated. It is found that the absence of crystalline drug material in solid dispersions containing nimodipine and polyethylene glycol 2000 is the prerequisite for a high dissolution rate and a remarkable supersaturation in the dissolution medium. Shock freezing during the preparation process, low storage temperatures and low relative humidities are identified to prevent recrystallisation. Furthermore, emphasis is put on the physico-chemical characterisation of solid dispersions. It is shown that the determination of crystallinity and dispersivity of the drug in solid dispersions can only be successful by combining different investigation methods like differential scanning calorimetry, hot stage microscopy, X-ray diffraction as well as macroscopic observation.