EFFECT OF PARTICLE-SIZE ON THE AVAILABLE SURFACE-AREA OF NIFEDIPINE FROM NIFEDIPINE-POLYETHYLENE GLYCOL-6000 SOLID DISPERSIONS

Solid dispersions containing 5%, 10%, 20%, 30% and 50% of nifedipine w ere prepared with polyethylene glycol (PEG) 6000 as carrier, respectiv ely, by the fusion method. Drug release from four different size fract ions of nifedipine-polyethylene glycol 6000 solid dispersions were exa mined. The probability parameters of Weibull distribution or log-norma l distribution could be obtained from linear regression of the dissolu tion data. The effects of particle size on the dissolution rate of nif edipine were evaluated in terms of the time course of the available su rface area (S(t)). The X-ray diffraction patterns showed that nifedipi ne was dispersed homogeneously in an amorphous state in the solid disp ersions with nifedipine concentration up to 10%. The initial values an d faster rate of decrease of S(t) during the dissolution process were markedly enhanced in the solid dispersions with lower contents of nife dipine (5% and 10%) due to the formation of high energy metastable (am orphous) states of the drug and differences in the particle sizes had little effect on the values of the available surface area and the diss olution of the drug. Values of available surface area were particle si ze dependent for the solid dispersions with higher contents of nifedip ine (20%, 30% and 50%) and the rate of decrease of S(t) was enhanced a s the particle size reduced.