Formulation and Release Kinetics of Neomycin Sulfate from a Polymeric Oil-in-Water Emulgel for Topical Application: A Proof-of-Concept Study

This proof-of-concept study aimed to develop and characterize a polymeric oil-in-water emulgel containing neomycin sulfate for topical application, using chitosan and methylcellulose as gelling agents, Tween 80 as emulsifier, and sweet almond oil as the oily phase. The novelty of the study lies in the formulation of a chitosan–methylcellulose oil-in-water emulgel for a highly hydrophilic aminoglycoside antibiotic, together with the integrated evaluation of its microstructure, rheological behavior, hydration capacity, and release kinetics. The formulation was evaluated in terms of physicochemical properties, microstructure, rheological behavior, short-term stability, drug content, and in vitro release performance. Rheological analysis showed pseudoplastic behavior, with apparent viscosity decreasing as the rotational speed increased, indicating suitable spreadability under applied stress. The neomycin sulfate content was 99.1 ± 0.7%, demonstrating efficient incorporation of the active substance. In vitro release testing showed a progressive release profile, reaching 70.1% of the theoretical drug content after 120 min. Kinetic analysis showed that the zero-order model gave the best empirical fit over the interval studied (R2 = 0.9980), while the Korsmeyer–Peppas exponent varied with the sampling points included and was therefore not used to support a specific transport mechanism. Because a single drug-loaded formulation was evaluated, without a placebo emulgel, a free-drug solution, or a comparator, the release profile cannot be attributed to the polymeric network as such; the results provide a preliminary basis for the further development of chitosan–methylcellulose emulgels as topical vehicles for neomycin sulfate.