Dissolution behaviour of nalidixic acid solid dispersions using water soluble dispersion carriers

The oral bioavailability of nalidixic acid (NA) is low due to its poor solubility and slow dissolution. Solid dispersions of NA containing varying concentrations of polyvinylpyrrolidone (PVP), beta-cyclodextrin (BCD) and sodium starch glycolate (SSG) were prepared by solvent evaporation technique in an attempt to improve dissolution rate of NA. Physical characterization of NA, physical mixtures (PM) and solid dispersions were investigated by a variety of analytical methods including scanning electron microscopy (SEM), infrared (IR) spectroscopy and powder X-ray diffraction (XRD). SEM was useful in the verification of possible nalidixic acid inclusion in the dispersion system by studying its surface and shape characteristics of different samples. IR analysis demonstrated no strong interaction between the drug and the carrier exists in the solid dispersions. The degree of crystallinity of nalidixic acid decreased and also differed with the dispersion systems of different carriers. Disolution studies indicated that the dissolution rate and percent dissolution efficiency (DE) were significantly increased in the solid dispersions compared with drug alone. The relative potency of the carriers to enhance the dissolution rate of nalidixic acid was in the order: BCD > PVP > SSG. The dissolution rate of the drug in the solid dispersions was faster when the ration of the drug to carrier was smaller. F-test suggests that first order model may be used for explaining the kinetics of drug release from all the solid dispersion systems.