Excipient toxicity and tolerability in self-emulsifying drug delivery systems: insights from cell-based assays

The toxicological evaluation of excipients plays a crucial role in the development of SEDDS. This study examined key formulation components to identify critical factors influencing cellular tolerance and supports the design of biocompatible SEDDS. Physicochemical properties of various oils, co-solvents, co-surfactants, non-ionic and charged surfactants formulated in SEDDS were determined via dynamic light scattering, while oxidative stability of selected surfactants was assessed through hydroperoxide quantification. Biological compatibility was evaluated by analyzing hemolytic effects on human erythrocytes and cell viability in CaCo-2 and HEK-293 cells. Metabolic activity and proliferation were additionally measured photometrically via MTT test. Cellular compatibility varied markedly among individual excipients, depending on their chemical structure and formulation role. In lipid-based systems, saturated triglycerides yielded up to sixfold higher viability than free fatty acids. Co-solvent toxicity correlated with lipophilicity and functional groups: isopropanol induced early membrane stress in CaCo-2 cells, while glycerol caused delayed hemolysis after 48  h. A clear structure-activity relationship emerged across surfactant types. PEG-based surfactants outperformed fatty alcohols and sugar-based formulations, which reached IC₅₀ values below 0.01% after 24  h and triggered early proliferation loss. This trend aligned with peroxide levels, as surfactants < 10  mM consistently maintained high CaCo-2 viability and stable IC₅₀ values, exemplified by polyoxyl 40 hydrogenated castor oil. Among zwitterionic surfactants, phosphatidylcholine showed highest biocompatibility, causing only a twofold reduction in hemolytic activity after 48  h, whereas cocoamidohydroxypropyl sulfobetaine induced an 12-fold decrease within 3  h. These findings underscore the role of excipient selection in minimizing cellular stress and adverse drug reactions in oral lipid-based drug delivery.