Solubility of LIDOCAINE in Ionic, Nonionic and Zwitterionic Surfactants

The solubility of an anesthetic drug, LIDOCAINE, in water was investigated in the presence of ionic, nonionic and zwitterionic surfactants at 25 °C, and the solubility was found to increase linearly with the surfactant concentration. The molar solubilization ratio, R _m,s, and Gibbs free energy, DG_s^o\Delta G_{\mathrm{s}}^{\mathrm{o}} values for nonionic surfactants fall in the order DDAO > Brij 35 > Brij 30, whereas for ionic and zwitterionic surfactants the order is DDAPS > DTAB > SDS. The high negative values of the Gibbs energies in the cases of DDAO and DDAPS prove them to be better surfactants for solubilizing this drug as compared to the other surfactants.