Abstract
The dissolution characteristics of solid dispersions with nicotinamide and hydroxypropylmethylcellulose (HPMC) as combined carriers were investigated in water, using nifedipine and nitrendipine as model drugs. The solid dispersions were obtained by the fusion method; after both drug and HPMC dissolved in the fused liquid of nicotinamide at 140°C, the fused mixtures were cooled to solidify them. For nifedipine solid dispersions, the supersaturation behavior was enhanced with a decrease in the viscosity or an increase in the weight fraction of HPMC. Nifedipine was present as an amorphous state even in the solid dispersion with a 1 : 3 : 0.2 weight ratio of drug : nicotinamide : HPMC. Also, the more the weight fraction of nifedipine increased, the more the formation of amorphous drug in solid dispersions was suppressed, thereby lowering the drug supersaturation level. Moreover, the effect of humidity during storage on the dissolution profiles of nifedipine solid dispersions was examined. The humidity caused crystallization of amorphous nifedipine in solid dispersions, and decreased the drug supersaturation level. For nitrendipine solid dispersions, similarly to the nifedipine system, amorphous nitrendipine was obtained in solid dispersions, and this led to the supersaturation phenomenon. However, the inhibitory effect of HPMC on the crystallization of nitrendipine from supersaturated solution was less than that for nifedipine; this is attributable to the lower solubility of nitrendipine crystals. Therefore, the drug dissolution of this ternary dispersion system was influenced by the viscosity and weight fraction of HPMC, the solubility and weight fraction of the drug and the humidity during storage.
