Reconstructed Human Epidermis: An Alternative Approach for In Vitro Bioequivalence Testing of Topical Products.

The use of in vitro human skin permeation tests is of value when addressing the quality and equivalence of topical drug products in Europe and the US. Human skin is the membrane of choice for these studies. The use of human skin as a membrane is hindered by limited access, high variability of results, and limited applicability for drugs with low skin permeability. Reconstructed human epidermis (RhE) models are validated as skin surrogates for safety tests and have been explored for percutaneous absorption testing. Clotrimazole poorly permeates human skin and is widely available for topical treatments. In this study, clotrimazole creams were used to test the ability of RhE to be used as biological membrane for bioequivalence testing, based on the Draft Guideline on Quality and Equivalence of Topical Products (CHMP/QWP/708282/2018) using a discriminative and modified in vitro permeation test (IVPT). To fulfill the validation of a discriminatory method, Canesten® 10 mg/g cream was compared with a test product with the same drug strength, along with two "negative controls" dosed at a 50% and 200% drug strength. Products were compared in finite dose conditions, regarding maximal flux (Jmax) and the total amount of drug permeated (Atotal). The results showed the discriminatory power of the method among the three drug strengths with no interference of the placebo formulation. The study design and validation complied with the requirements established in the guideline for a valid IVPT. This new test system allowed for the equivalence comparison between test and comparator product. Higher permeability of the RhE compared to human skin could be observed. This arose as a strength of the model for this modified IVPT bioequivalence testing, since comparing permeation profiles among products is envisaged instead of drawing absolute conclusions on skin permeation extent. These results may support the acceptance of RhE as biological membranes for modified IVPT in bioequivalence testing of topical products.

SkinEthic™ RHE for in vitro evaluation of skin irritation of medical device extracts.

According to ISO 10993 standards for biocompatibility of medical devices, skin irritation is one of the three toxicological endpoints to be always addressed in a biological risk assessment. This work presents a new protocol to assess this endpoint in vitro rather than in vivo. The protocol was adapted to medical devices extracts from the OECD TG 439 with the SkinEthic™ RHE model as test system. It was challenged with irritant chemicals, Sodium Dodecyl Sulfate, Lactic Acid and Heptanoic Acid spiked in polar solvents, sodium chloride solution or phosphate buffer saline and non-polar solvent, Sesame Oil. Cell viability measured by MTT reduction after 24 h exposure was used as readout. Quantification of IL-1α release as secondary readout did not increased performance. Samples of heat-pressed polyvinyl chloride (PVC) and silicone sheets infused with or without known irritant (4% Genapol-X80, 6% Genapol-X100 and 15% SDS) were tested after extraction in polar and non-polar solvents. Medical device extracts are classified irritant when the cell viability is inferior or equal to 50%, compared to the negative controls tissues, in at least one extraction solvent. The correct classification of all the samples confirmed the good performance of this new protocol for in vitro skin irritation of medical devices extracts with the SkinEthic™ RHE model. Seven naïve laboratories were trained in prevision of the Round Robin Study to evaluate Reconstructed Human Epidermis (RhE) models as in vitro skin irritation test for detection of irritant potential in medical device extracts.