Impact of Porcine Ear Skin Processing on Metformin Lotion Permeation In Vitro

Porcine ear skin is widely used as a surrogate for human skin in in vitro permeation testing (IVPT) due to its structural and physiological similarities. However, commercial sourcing from the food industry often involves scalding, dehairing, and other processing steps that damage key layers of the skin barrier, potentially altering drug diffusion. Despite this, procurement and preparation methods are rarely standardized or reported in detail. In this study, we investigated how pork harvest processing affects the permeation of a topical 6% metformin lotion (ML) formulated with glycerol or glycerol plus propylene glycol. Permeation was evaluated using Franz diffusion cells over 48 hours, and skin structure was examined histologically. Processed porcine skin exhibited dramatically higher metformin flux — up to 20–60× greater within 2 hours — and cumulative diffusion (approximately 80% at 48 hours) compared to intact skin, which retained strong barrier function (< 30% total diffusion). Histology confirmed that pork harvest processing removed the stratum corneum and viable epidermis, facilitating rapid drug penetration. These findings demonstrate that commercially processed porcine skin is not an appropriate surrogate for human skin in permeation studies and highlight the critical need for standardized sourcing, documentation, and barrier integrity assessment in IVPT research.