In vitro selection and efficacy of topical skin protectants against the nerve agent VX.

Against highly toxic chemicals that are quickly absorbed in the skin, topical formulations could adequately complement specific protective suits and equipments. In this work, we evaluated in vitro and compared the skin protection efficacy against the nerve agent VX of four different topical formulations: oil-in-water and water-in-oil emulsions, a perfluorinated-based cream and a hydrogel. Semi-permeable silicone membrane, pig-ear and human abdominal split-thickness skin samples mounted in diffusion cells were compared as in vitro permeation tests. The results showed that silicone membrane could be used instead of skin samples to screen for potentially effective formulations. However, the results indicated that due to potentially significant interactions between formulations and skin, relevant ranking of formulations according to their protective efficacy could require tests with skin samples. The main phase of emulsions, water or oil, was not found to be critical for skin protective efficacy against VX. Instead, specific film-forming ingredients such as perfluorinated-based polymers and silicones could significantly affect the skin protective efficacy of formulations. We showed that a hydrogel containing specific hydrophilic polymers was by far the most effective of the formulations evaluated against VX skin permeation in vitro.

Evaluation of in vitro tests to assess the efficacy of formulations as topical skin protectants against organophosphorus compounds.

Prevention of exposure to the neurotoxic organophosphorus compounds (OP) is a major concern both for pesticide users and soldiers. Skin barrier creams are being developed to complement or replace uncomfortable chemical protective suits. Quick evaluation of formulations efficacy mainly relies on in vitro tests which lead to consistent, complementary and relevant results. The objectives of this work were to determine the consistency of results from in vitro tests and importance of the formulation composition in the skin protective efficacy. The efficacy of three formulations, i.e. oil-in-water and water-in-oil emulsions and perfluorinated compounds-based cream, was evaluated against the OP paraoxon in vitro. Our results indicated that the least effective formulations could be quickly identified by performing in vitro permeation tests with silicone membrane and by evaluating interfacial interactions between formulations and OP. Among the tested formulations, the perfluorinated compounds-based cream could have a broader spectrum of efficacy than emulsions against OP and other toxic chemicals.