In brief, 200 μL of 4 mg/mL loperamide HCl-encapsulated liposome suspension (equivalent to 0.8 mg loperamide HCl) was mixed with 1 mL of carbopol gel (0.5%, w/w) and added in a dialysis bag (MWCO 10 kDa; Thermo Fisher Scientific). The dialysis system was suspended in a release volume of 40 mL PBS, pH 6.5, at 37°C and rotated at 200 rpm. For control groups, 0.8 mg of loperamide HCl was mixed with 1 mL of carbopol gel (0.5%, w/w) and placed in a dialysis bag. Stability was assessed using the dialysis method described. The drug-loaded gel was spread thinly onto the membrane surface within the dialysis tubing to mimic topical administration. At scheduled intervals, 200 μL of the release medium was collected for the HPLC assay. The same volume of fresh PBS buffer at the same temperature was added immediately to maintain constant release volume. The length of the dialysis tubing was kept consistent for all methods to ensure that the surface area available for dialysis remained constant.