Effect of the Interaction Between an Ionic Surfactant and Polymer on the Dissolution of a Poorly Soluble Drug
Surfactants are commonly incorporated in conventional and enabled formulations to enhance the rate and extent of dissolution of drugs exhibiting poor aqueous solubility. Generally the interactions between the drug and excipients are systematically evaluated, however, limited attention is paid towards understanding the effect of interaction between functional excipients and its impact on the performance of the product. In the current study, the effect of potential interaction between a nonionic polymer binder, povidone, and anionic surfactant docusate sodium on the rate and extent of dissolution of a drug exhibiting poor aqueous solubility was evaluated by varying the proportions of the binder and the surfactant in the formulation. Potential complexation or aggregation between the excipients was investigated by fluorescence spectroscopy and zeta potential measurements of the aqueous solutions of docusate sodium, povidone, and sodium lauryl sulfate (SLS). The rate and extent of drug release was found to decrease with an increase in the proportion of docusate sodium and povidone in the formulations. Difference in magnitude of surface charge (zeta potential) of docusate sodium in presence of povidone indicated potential surfactant-polymer aggregation during dissolution which was corroborated by CAC/CMC values derived from fluorescence spectroscopic measurements. The decrease in the rate of drug release was attributed to an increase in the viscosity of the microenvironment of dissolving particles due to the interaction of docusate sodium and povidone in the aqueous media during dissolution. These findings highlight the importance of systematic evaluation of the interaction of ionic surfactants with the polymeric components within the formulation to ensure the appropriate selection of the type of surfactant as well as its proportion in the formulation.
Conclusion
Use of surfactants in formulations is proven to enhance the dissolution rate of poorly water soluble drugs. The rate and extent of dissolution is expected to increase with an increase in the proportion of the surfactant; however, the rate of drug release was found to decrease as the proportion of
anionic surfactant, docusate sodium, in the formulation increased. The decrease in the rate of release was attributed to an increase in the viscosity of the microenvironment of dissolving particles caused by interaction of the ionic surfactant with the polymeric binder (povidone) in the aqueous
media during dissolution. Therefore, in addition to binary drug excipient compatibility studies, prudent evaluation of the interaction of ionic surfactants with polymeric components within the formulation is necessary to ensure the selection of an appropriate type and concentration of the surfactant, and consequently, to avoid unexpected impediments in the development process.