Influence of Different Polymers on the Crystallization Tendency of Molecularly Dispersed Amorphous Felodipine

The ability of various polymers to inhibit the crystallization of amorphous felodipine was studied in amorphous molecular dispersions. Spin-coated films of felodipine with poly(vinylpyrrolidone) (PVP), hydroxypropylmethylcellulose acetate succinate (HPMCAS), and hydroxypropylmethylcellulose (HPMC) were prepared and used for measurement of the nucleation rate and to probe drug-polymer intermolecular interactions. Bulk solid dispersions were prepared by a solvent evaporation method and characterized using thermal analysis. It was found that each polymer was able to significantly decrease the nucleation rate of amorphous felodipine even at low concentrations (3-25% w/w). Each polymer was found to affect the nucleation rate to a similar extent at an equivalent weight fraction. For HPMC and HPMCAS, thermal analysis indicated that the glass transition temperature (Tg) of the solid dispersions were not significantly different from that of felodipine alone, whereas an increase in Tg was observed for the PVP containing solid dispersions. Infrared spectroscopic studies indicated that hydrogen bonding interactions were formed between felodipine and each of the polymers. These interactions were stronger between felodipine and PVP than for the other polymers. It was speculated that, at the concentrations employed, the polymers reduce the nucleation rate through increasing the kinetic barrier to nucleation.