Optimizing Self-Emulsifying Drug Delivery Systems for the Oral Delivery of a Hydrophobic Ion-Paired Lysozyme Complex

<b>Background</b>: The oral delivery of biopharmaceuticals remains a major challenge for researchers and the pharmaceutical industry. Therefore, extensive research is ongoing to develop a viable delivery method, hence self-emulsifying drug delivery systems (SEDDSs) are being investigated because of their ability to protect the carried macromolecules in the gastrointestinal environment and facilitate absorption through the intestinal barrier. <b>Objectives</b>: To systematically investigate this promising method for the oral delivery of lysozyme (LYZ) and to model oral peptide/protein administration. <b>Methods</b>: LYZ/sodium dodecyl sulfate (SDS) hydrophobic ion pairs (HIPs) were prepared to enhance protein solubility and stability in SEDDSs. Different surfactants (Tween^® 20 and 80) and as co-surfactants (Span^® 20 and 80) were combined for the preparation of liquid SEDDSs according to a 2² full factorial design and samples of each combination were formulated based on a three-factor-constrained mixture design. The critical quality attributes (CQAs), droplet size, polydispersity index (PDI), and zeta potential were measured by dynamic light scattering (DLS). The process design space was determined by response surface methodology (RSM) and two-dimensional ternary contour plots. An in vitro release test was performed using the sample-and-separate approach. <b>Results</b>: Emulsions of SEDDSs with the optimal properties of droplet size < 200 nm, PDI < 0.4 and zeta potential < -10 mV were prepared. Consequently, a HIP load of 10 mg/g was achievable, exhibiting apparent first-order kinetics, with approximately 80% of the loaded LYZ released within 6 h. <b>Conclusions</b>: This study may contribute to better understanding of the effects and interactions of formulating materials for SEDDSs and their possible role in the oral delivery of biopharmaceuticals.