Enhancement of nalidixic acid solubility via cosolvency and solid dispersion

Nalidixic acid is practically insoluble in water therefore the aim of this study was to study the effect of both cosolvency and solid dispersion on its solubility. Among different cosolvents, the highest result was achieved by isopropanol (30 % v/v). Through all studied solid dispersion carriers in the ratio 1:1, sodium benzoate enhanced both the solubility and antibacterial activity of nalidixic acid and was therefore selected for further investigation. Increasing sodium benzoate ratio had significantly increased nalidixic acid solubility till a 1:8 ratio. Differential scanning calorimetry (DSC) showed a sharp endothermic peak of nalidixic acid which was slightly shifted to lower temperature accompanied by significant broadening in the case of solid dispersion. Further confirmation was obtained by X-ray powder diffraction (XRPD) whereas the peak heights were much reduced in the case of solid dispersion confirming the cause of increasing solubility.