Iodine, a nonmetallic element that forms salts with most other elements, has germicidal activity.
Iodine solution and tincture are used topically as antiseptics in the management of minor, superficial skin wounds and have been used to disinfect the skin preoperatively.
Iodine solution and tincture are applied topically to the affected areas as necessary; to avoid irritation, surfaces to which the preparations are applied should not be covered.
Iodine has a low order of toxicity when applied topically as a 2% solution. Iodine solutions may stain the skin, irritate tissues (e.g., iodine burn), and cause sensitization in some individuals. Iodine burns have mainly been associated with use of a 7% hydroalcoholic solution of the drug. Hydroalcoholic solutions of the drug are more irritating (i.e., stinging sensation) than aqueous solutions. Because iodine may cause burns on occluded skin, an iodine-treated wound should not be covered with a tight bandage.
Sodium thiosulfate inactivates iodine and is an effective chemical antidote for iodine poisoning. Solutions of sodium thiosulfate may be used to remove iodine stains from skin and clothing.
Iodine is a local irritant and has germicidal activity. As a germicide, iodine has a wide spectra of activity including bactericidal activity against gram-positive and gram-negative bacteria and fungicidal, protozoacidal (e.g., trichomonocidal), cysticidal, virucidal, and some sporicidal activity. The drug is a potent and rapidly acting germicide. Elemental iodine and, to a lesser extent (since it is present in lower concentrations compared with elemental iodine at the pH and concentration generally used), hypoiodic acid are principally responsible for the germicidal activity of the drug. (See Chemistry and Stability.) On a weight basis, elemental iodine is 2-3 times as cysticidal and 6 times as sporicidal as hydroiodic acid, and hydroiodic acid is at least 40 times as virucidal as elemental iodine; it has been suggested that this difference in activity against these organisms results from the greater diffusibility of elemental iodine through cell walls of cysts and spores and the greater oxidizing potency of hydroiodic acid (against viruses).
Elemental iodine readily penetrates the cell wall of microorganisms. Although the precise mechanism of iodine's germicidal activity has not been determined, it has been suggested that iodine has a lethal effect on microorganisms by reacting with basic NH groups present on amino acids (e.g., lysine, histidine, arginine) and on the bases of nucleotides (e.g., adenine, cytosine, guanine) forming the corresponding N -iododerivatives; by oxidizing the sulfhydryl (SH) group of cysteine, resulting in disruption of protein synthesis; by reacting with the phenolic group of tyrosine, resulting in steric hindrance in hydrogen bonding involving this amino acid; and by reacting with carbon-carbon double bonds of unsaturated fatty acids, resulting in disruption of the physical properties of lipids. Iodine, like other halogens, also reacts with dead microorganisms and with other organic matter (e.g., proteins), resulting in compounds or complexes that reportedly have weaker germicidal activity or no activity. In the presence of organic matter, some elemental iodine is bound covalently, but most is loosely complexed with the organic matter and then slowly released. Iodine reportedly reacts more slowly with proteins than chlorine or bromine and therefore is a more effective germicide than these other halogens when organic matter is present.
Various values for the minimum concentration at which iodine is lethal to cells have been reported. However, it is difficult to draw any conclusions regarding these values since environmental conditions (e.g., pH, temperature, concentration and type of iodine preparation, time of exposure to the drug, amount and type of organic and inorganic substances present) varied considerably. Generally, a 2% hydroalcoholic solution of iodine is considered effective as a topical antiseptic for small, minor wounds.
Iodine is a nonmetallic element that forms salts with most other elements. Iodine occurs as heavy, grayish black plates or granules and has a metallic luster and a characteristic odor. Iodine is very slightly soluble in water and soluble in alcohol and in solutions of iodides. Iodine topical solution is an aqueous solution containing 1.8-2.2 g of iodine and 2.1-2.6 g of sodium iodide in each 100 mL. Iodine tincture is a hydroalcoholic solution containing 1.8-2.2 g of iodine and 2.1-2.6 g of sodium iodide in each 100 mL; the tincture contains 44-50% alcohol. Iodine topical solution and tincture are transparent, reddish brown liquids having the odor of iodine; the tincture also has the odor of alcohol.
In aqueous solutions, iodine is present as 7 different species: elemental iodine (I2), hypoiodic acid (HOI), iodine cation ([H2OI]+), triiodide ion (I3-), iodide ion (I-), hypoiodite ion (OI-), and iodate ion (IO3-). Elemental iodine, hypoiodic acid, and iodine cation have potent germicidal activity; triiodide and hypoiodite ions are weak oxidants exhibiting weak antibacterial activity, and iodide ion has no antimicrobial activity. Iodate ion has antimicrobial activity only at a pH less than 4, and therefore generally does not contribute to the germicidal activity of iodine. In aqueous solutions containing 12.7 mg of iodine per 100 mL, 79.9 or 99.2% of total iodine is calculated to be present as elemental iodine at a pH of 7.5 or 4.5, respectively.
Iodine topical solution should be stored in tight, light-resistant containers at a temperature not exceeding 35°C, and iodine tincture should be stored in tight containers.
Additional Information
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