Abstract
The chemical and physicochemical stability of nifedipine in nifedipine-polyvinylpyrrolidone (PVP) coprecipitate systems was studied. It was found that nifedipine in the coprecipitate systems was chemically stable to heat and humidity. Storage of the coprecipitate systems under humid conditions was found to influence the dissolution behavior. The X-ray diffraction pattern of coprecipitate which had been stored under very humid conditions showed many sharp peaks attributable to nifedipine crystals. It is suggested that the inferior dissolution of the humidly stored coprecipitate systems resulted from the partial crystallization of amorphous nifedipine in the PVP matrix. Correlations between the in vitro dissolution behavior and the in vivo bioavailability parameters following oral administration to dogs were studied to confirm the effect of storage on the bioavailability. It was concluded that coprecipitate systems of nifedipine with PVP should be stored in such a way that they are not exposed to humidity so as to avoid a decrease of drug bioavailability.
