Scientists tested different ingredients to help a synthetic hormone peptide (buserelin) pass through the vaginal wall. They built a precise lab test to measure how much gets through and found that chitosan, a natural polymer, works best at boosting absorption in pig tissue.

<b>Background/Objectives</b>: This study aimed to enhance the vaginal permeation of buserelin acetate (BA), a synthetic gonadotropin-releasing hormone (GnRH) analogue, by evaluating various permeation enhancers (PEs) using a validated reversed-phase high-performance liquid chromatography (RP-HPLC) method and an ex vivo porcine vaginal model. <b>Methods</b>: A robust RP-HPLC method was developed and validated according to ICH Q2 (R2) guidelines to enable accurate quantification of BA in permeation samples. The analytical method demonstrated high specificity, linearity (R² = 0.9999), accuracy (98-102%), precision (%RSD &lt; 2%), robustness, and stability. Using this method, ex vivo permeation studies were conducted with six different PEs: 2-hydroxypropyl-&#x3b2;-cyclodextrin, sodium dodecyl sulfate, poloxamer 188, Span 80, Tween 80, and chitosan. <b>Results</b>: Among all tested PEs, chitosan demonstrated the best enhancement of BA permeation. It achieved the highest flux (J) (0.64 &#xb1; 0.03 &#xd7; 10^-2 &#xb5;g/cm²&#xb7;h) and apparent permeability coefficient (P_app) (16.20 &#xb1; 0.84 &#xd7; 10^-5 cm/h), both of which were statistically significantly higher (<i>p</i> &lt; 0.05) than those of all other enhancer groups. Kinetic modelling indicated a non-Fickian, biphasic permeation mechanism best described by the Makoid-Banakar model. <b>Conclusions</b>: These findings highlight chitosan's potential as an effective intravaginal delivery vehicle for peptide therapeutics and establish the validated HPLC method as a reliable platform for future formulation development and translational studies in mucosal drug delivery.