Testing vaginal irritation with the Hen’s Egg Test-Chorioallantoic Membrane assay

The HET-CAM (Hen’s Egg Test-Chorioallantoic Membrane) assay is an in vitro alternative to the in vivo Draize rabbit eye test. This qualitative method assesses the irritancy potential of chemicals. The chorioallantoic membrane responds to injury with an inflammatory process similar to that in the rabbit eye’s conjunctival tissue. Regarding topical toxicity assessment of medical devices, ISO 10993-10 states that any skin or eye irritant material shall be directly labelled as a potential vaginal irritant without animal testing, suggesting that the irri­tation potentials for the eye and the vaginal epithelia are similar. The aim of this work was to apply the HET-CAM assay to test the irritancy potential of vaginal formulations. Vaginal semisolid medicines and lubricants currently marketed were tested along with the Universal Placebo formulation that has been shown to be clinically safe. Nonoxynol-9 (N-9), a known vaginal irritant, was enrolled as positive control (concentrations ranging from 0.001 to 100% (v/v)). The assay was conducted according to the ICCVAM – Recommended Test Method (NIH Publication No. 10-7553 – 2010). Formulations were then classified according to irritation score (IS), using the analysis methods (A) and (B). The studied vaginal formulations showed low potential for irritation. N-9 was classified as a severe irritant at concentrations above 2%, which is in line with clinical data, envisaging a possible in vitro/in vivo correlation. IS (B) was considered a more detailed classification output. Although still requiring further validation, the HET-CAM assay seems an ideal prospect for in vitro vaginal irritancy testing.