Release Characteristics of Nifedipine Sustained-Release Granules in Vitro and in Healthy Subjects

The release characteristics of nifedipine sustained-release granules, composed of ethylcellulose, hydroxypropylmethylcellulose and corn starch, were examined in vitro as well as in healthy subjects. The release of nifedipine from the granules in vitro was not first-order, but a linear relationship up to about 40% release was obtained based on the Higuchi equation. The release rate was not strongly influenced by pH, stirring speed, surfactant or ionic strength. These granules were administered to healthy subjects and the plasma levels of nifedipine were compared with those after administration of nifedipine soft gelatin capsule. Plasma levels following the administration of the granules were prolonged as compared with those in the case of the soft gelatin capsule, and plasma levels of about 13 ng/ml at 12 h post-dosing were detected. The known problem of marked inter-subject variability of the plasma levels was not encountered after administration of the sustained-release granules, presumably due to the multiple-units dosage form and the established low sensitivity of the drug release rate to the in vitro environment, i.e., pH, stirring speed, surfactant and ionic strength.