Clinicians have utilized iodine-based compositions to treat a wide range of human diseases. Early uses included treatment of goiter by Coindent in 1820 and syphillus by Lugol in 1831. Since 1950 most of the innovative medical studies with iodine rely upon the use of povidone-iodine, which is a topical disinfectant. The types of indications that have been studied with povidone-iodine include skin diseases, gingivitis/oral mucositis, and various ocular diseases. Unfortunately, povidone-iodine contains very low concentrations of molecular iodine (1 to 3 ppm) and very high concentrations of other inactive iodine species (>10,000 ppm). In pharmaceutical terms the “therapeutic index” of povidone-iodine is very low. The therapeutic index of a drug is the ratio of the largest safe dose to the smallest effective dose.
The lack of a suitable formulation of molecular iodine has not prevented physicians from exploring its potential to treat a range of indications with povidone-iodine. Unfortunately, the use of povidone-iodine limits the concentration of the active, molecular iodine, and increases staining and irritation. Despite povidone-iodine’s unoptimized composition, several published studies indicate that molecular iodine has potential therapeutic utility in several clinical settings.
Use of Molecular Iodine on Skin
Symbollon is has developed a topical formulation of molecular iodine, we refer to as IoDerm, and is preparing to submit an IND to the FDA based upon this composition. IoDerm is a topical gel formulation that provides molecular iodine upon admixture. IoDerm is the first of a new class of iodine-based topical formulations that will not stain skin but provides over 100 times more biocidal iodine than traditional iodophors. We believe this improved therapeutic index will allow IoDerm to address several unmet market needs.
An essential rationale for the use of molecular iodine to treat skin diseases is the observation that molecular iodine readily penetrates into skin and remains biocidal while it diffuses therein. Gottardi has examined the interaction of 10%-polyvinylpyrrolidone (PVP) and Lugol’s solution with skin. A comparison was made between an aqueous solution containing 170 ppm of molecular iodine and 10% PVP which contains approximately 5 ppm of molecular iodine; 10,000 ppm of tri-iodide; and 6,600 ppm of iodide.
Gottardi W. The uptake and release of molecular iodine by the skin: chemical and bactericidal evidence of residual effects caused by povidone-iodine. J. Hosp. Infect. 1995;29:9-18.
Approximately 40 times more molecular iodine was absorbed by skin with the 170 ppm of the aqueous molecular iodine composition than with 10% PVP. Gottardi concluded that molecular iodine is the only form of iodine that is absorbed into skin. The extent of topical absorption is effected by the following parameters: (1) the concentration of molecular iodine; (2) the contact time; (3) the dimensions of the treated area; and (4) the nature of the treated skin. Gottardi was able to demonstrate out-gassing of molecular iodine from skin by both direct chemical measurement and microbiological assessment for up to 24 hours after application. This observation suggests that skin can serve as a reservoir for molecular iodine and that molecular iodine remains stable (i.e., biocidal) while diffusing therein.
Povidone-iodine has been used to treat acne vulgaris, ringworm versicolor, pityriasis versicolor, and cold sores from herpes simplex virus. The concentration of molecular iodine in these formulations was not measured. In each of these disease states molecular iodine was reported to exhibit a beneficial effect.
Brown EJ. A povidone-iodine skin cleanser foam in the management of acne vulgaris. Brit. J. Clin. Practice 1977;31:218-9.
Khan SA. Observations in the treatment of acne vulgaris with a povidone iodine skin cleanser. Brit. J. Clin. Practice 1979;33:289-90.
Antimicrobial Applications
