Quantifying skin permeation of a novel metformin lotion using modified hydrophilic interaction liquid chromatography

<b>Aim:</b> This study aimed to quantify the permeation of metformin (Met) lotion through pig ear skin using high-performance liquid chromatography, specifically hydrophilic interaction liquid chromatography (HILIC), to separate Met from biological contaminants and effectively measure its permeation through skin similar to human skin.<b>Materials & methods:</b> A Franz cell permeation assay was used to assess the permeation kinetics of 6% Met lotion through pig ear skin. Samples were collected at various time points and prepared for high-performance liquid chromatography analysis by removing large biological contaminants. The permeated Met was quantified by monitoring its retention time (RT) at 9 min using HILIC, with an acidic, polar mobile phase and a normal-phase column.<b>Results:</b> A distinct Met peak with a RT of approximately 9 min was observed in the 6% Met lotion, which was absent in the permeation samples from the 0% Met lotion. This peak (RT 9 min) was distinct from the 'biological-contaminants' peaks at RT 2-3 min and increased linearly over time, reaching 36.8% of the total applied Met at 24 h.<b>Conclusion:</b> These findings demonstrate that the HILIC method effectively separates Met from biological components in pig ear skin, allowing accurate quantification of Met despite the presence of skin lipids and proteins.