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Abstract: Evaluating toxicity of bad stuff adsorbed by contacts

This is kind of an interesting piece... about methodologies for figuring out to what extent things toxic ingredients (such as benzalkonium chloride, a common preservative in prescription eyedrops) are adsorbed by certain contacts and may pose safety issues.

Thin, gel-like, hydrated soft contact lenses are directly placed on human eyes and can be used with a variety of eye drops containing over-the-counter drugs, even though some labels suggest caution. In this study, evaluation was carried out of the cytotoxic potential of soft contact lenses that had adsorbed the active ingredients of over-the-counter eye drops. Although there are some guidelines for in vitro cytotoxicity tests for preclinical biological evaluation of medical materials and devices, the shape of soft contact lenses makes these tests difficult to apply. We developed a new cytotoxicity test in which cored lenses 6 mm in diameter were pretreated with active ingredients and placed in direct contact with Chinese hamster lung V79 cells. Among the 11 chemicals tested, anionic and hydrated type-IV lenses that had been soaked in benzalkonium chloride, berberine chloride, and chlorhexidine indicated cytotoxic potential toward the cultured cells. Solutions of 0.002%-0.004% benzalkonium chloride, 0.025% berberine chloride, and 0.008% chlorhexidine were not cytotoxic to the cultured cells under the experimental conditions; however, type-IV lenses that had been immersed in the same concentrations of these active ingredients showed significant cytotoxicity to the cultured cells. These results suggest that cytotoxicity to the ocular surface may be caused by soft contact lenses that have been soaked in the usual ranges of nontoxic eye drops containing benzalkonium chloride, berberine chloride, and chlorhexidine. This modified in vitro safety test system for cored soft contact lenses is of use for evaluating the cytotoxic potential of ophthalmological drugs adsorbed on soft contact lens surfaces.

J Toxicol Sci. 2012;37(3):639-43.
Pharmaceutical Research Laboratories No. 1, Research & Development Headquarters, Lion Corporation.
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