Povacoat affecting solid-state polymorphic changes of indomethacin after co-evaporation from different types of solvents via conventional and microwave drying techniques

Abstract

The effect of Povacoat on the solid state characteristics and polymorphic transformation of γ-form of indomethacin (γ-IMC) after solvent co-evaporation via two drying methods was investigated by thermoanalytical and FTIR spectroscopic studies. The types of solvents (water, ethanol, and water:ethanol (1:9 ~ 2:8, v/v)), weight ratios of Povacoat:IMC (4:1 ~ 4:10, w/w), and drying methods (air-drying and microwave-drying) were selected as variables in this study. A physical mixture of Povacoat and γ-IMC was also carried out by neat grinding process. The results indicate that there was no interaction between Povacoat and γ-IMC or no polymorphic change of γ-IMC after the neat co-grinding process. Since Povacoat was only soluble in water or <30% ethanol aqueous solution but γ-IMC was only soluble in organic solvents, different solvents and drying methods might significantly influence the solid-state characteristics of IMC formed in the presence of Povacoat. It was found that the amorphous IMC was formed in the Povacoat/IMC evaporates after dissolving both Povacoat and γ-IMC in water:ethanol (mixed ratio=1:9 and 2:8, v/v) and co-evaporation via microwave-drying, whereas the α-IMC was formed in the Povacoat/IMC evaporates via the air-drying method. In addition, the predominate α-IMC formation was only found in all the Povacoat/IMC evaporates with different weight ratios prepared by previously dissolving in water:ethanol (1:9, v/v) and co-evaporation via air-drying, but the amorphous IMC formation after co-evaporation via microwave-drying was obtained except the 4:10 (w/w) weight ratio. The thermal effect of microwave irradiation and the presence of Povacoat might be responsible for the amorphous IMC formation in the Povacoat/IMC evaporates.