The hydrolysis of indomethacin in aqueous solutions of polysorbates

The effect of surfactants on the rate of hydrolysis of indomethacin is reported for homologous series of polyoxyethylene (20) sorbitan fatty acid esters (polysorbates). The degradation of the solubilized drug follows a first-order process in which the rate decreases with the increasing surfactant concentration. The increasing length of hydrophobic chain of surfactant molecule has little effect on the rate of reaction. The solubilized solutions of indomethacin can be stored for at least one year. The influence of pH on the solubilizing power of polysorbate 80 is also studied.