Physicochemical characterization and drug release studies of nilvadipine solid dispersions using water-insoluble polymer as a carrier.

Nilvadipine solid dispersions were prepared by the solvent method using water-insoluble polymers, including low-substituted hydroxypropylcellulose, croscarmellose sodium, carmellose calcium, carmellose, and crospovidone. Differential scanning calorimetry and powder x-ray diffraction analysis showed that nilvadipine was present in an amorphous state in the solid dispersion obtained using crospovidone as a carrier. The degree of crystallinity of nilvadipine was dependent on the ratio of nilvadipine to crospovidone, and nilvadipine was present in an amorphous state when the ratio of nilvadipine to crospovidone was below one-half. Fourier transform infrared studies suggested the presence of hydrogen bonding between nilvadipine and crospovidone in the solid dispersion. Dissolution studies indicated that the maximum percentage of dissolution and dissolution rate constants were markedly increased in nilvadipine with crospovidone solid dispersion, compared with those of pure nilvadipine and physical mixtures. The dissolution rate of nilvadipine solid dispersion with crospovidone could be calculated by the Higuchi square root time equation.