Evaluation of the Crystal Growth Rate of Felodipine Polymorphs in the Presence and Absence of Additives As a Function of Temperature

Abstract

The purpose of the present study was to compare the effect of temperature and a polymeric additive, poly(vinyl pyrrolidone) (PVP), on the crystal growth rate of two polymorphs of felodipine from amorphous samples. Comparing the growth rates of the two polymorphs in the presence of PVP should provide mechanistic information on whether PVP inhibits crystal growth of felodipine by interacting at the crystal surface of felodipine or in the amorphous regions. Optical microscopy was used to measure the growth rates at various temperatures in the range of 18–100 °C for the form I polymorph and 40–100 °C for the form II polymorph. Both surface and bulk growth rates for the form I polymorph were evaluated, while for the form II polymorph, only the bulk growth rate could be studied. No difference in the growth rate between surface and bulk crystals of form I was observed at higher temperatures (>70 °C). However, below 65 °C the surface crystal growth rate was faster than the bulk crystal growth rate. Another mode o...