Prediction of Satranidazole Solubility in Water-Polyethylene Glycol 400 Mixtures Using Extended Hildebrand Solubility Approach

       The Extended Hildebrand Solubility Parameter Approach (EHSA) is used to estimate the solubility of satranidazole in binary solvent systems. The solubility of satranidazole in various water-PEG 400 mixtures was analyzed in terms of solute-solvent interactions using a modified version of Hildebrand-Scatchard treatment for regular solutions. The solubility equation employs term interaction energy (W) to replace the geometric mean (δ1δ2), where δ1 and δ2 are the cohesive energy densities for the solvent and solute, respectively. The new equation provides an accurate prediction of solubility once the interaction energy ‘W’ is obtained. In this case, the energy term is regressed against a polynomial in δ1 of the binary mixture. A quartic expression of ‘W’ in terms of solvent solubility parameter was found for predicting the solubility of satranidazole in water-PEG 400 mixtures. The expression yields an error in mole fraction solubility of ~2.17%, a value approximating that of the experimentally determined solubility. The method has potential usefulness in pre-formulation and formulation studies during which solubility prediction is important for drug design.