Topical Molecular Iodine: An Optimal Biocide Constrained by Inadequate Formulations

The only biocidal iodine species in topical iodine disinfectants is molecular iodine (I2). I2, a biomolecule, has broad-spectrum antimicrobial activity and does not generate resistance. Physicians, regulatory agencies, and scientists have assumed that I2 is responsible for the skin staining and irritation associated with the clinical use of iodine disinfectants; this assumption is deeply embedded in the medical community but is not supported with empirical data. This study provides the first experimental data that measure the biocompatibility of I2 with human skin. Human skin explants in tissue culture were evaluated at 3, 7, and 24 h after being exposed to I2 (500 to 15,000 ppm). Cell viability was measured relative to phosphate-buffered saline using 3-[4,5-dimethylthiazol-2yl]-2,5-diphenyl-tetrazolium bromide (MTT). The biocidal activity of I2 vapor emitted from silicone was demonstrated against bacteria growing on agar to confirm I2 off-gassing from skin was an active biocide. Additionally, statistically significant bacterial reductions with both gas and solution phase I2 were observed in a static and dynamic five-species wound biofilm. The data suggest that high, e.g., 50–5000 ppm, levels of I2 should be incorporated into topical iodine disinfectants instead of the very low (0.2–10 ppm) levels found in 10% povidone iodine products currently in use.