Inhibitory Effect of 2-Hydroxypropyl-β-cyclodextrin on Crystal-growth of Nifedipine During Storage: Superior Dissolution and Oral Bioavailability Compared with Polyvinylpyrrolidone K-30

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Abstract
To prevent the crystal-growth of nifedipine during storage, 2-hydroxypropyl-β-cyclodextrin (HP-β-CyD) was employed as a hydrophilic drug carrier and compared with polyvinylpyrrolidone K-30 (PVP). Amorphous nifedipine powders were prepared by spray-drying with HP-β-CyD or PVP, and their crystal-growing behaviour at accelerated storage conditions were examined by X-ray diffraction analysis and microscopy. Although PVP initially retarded the crystallization of nifedipine, it failed to control the increase of crystal size after prolonged storage at 60°C., 75% r.h., resulting in a remarkable decrease in dissolution rate in water. In sharp contrast, a relatively fine and uniform size of nifedipine crystals was maintained in the HP-β-CyD system even after accelerated storage conditions. The enhanced dissolution observed for all the HP-β-CyD systems in a dissolution medium containing 0·1% non-ionic surfactant HCO-60 were clearly reflected in the in-vivo absorption of nifedipine following oral administration to dogs. These results suggest that HP-β-CyD is particularly useful in solving problems encountered on storage of amorphous nifedipine in solid dosage forms.