Elemental iodine (I2) is probably the oldest germicide still in use today. It was listed in 1830 in USP-II as a tincture and a liniment. Iodine tincture (2% iodine in 50% alcohol with sodium iodide), strong iodine solution (Lugol's solution, 5% iodine in water with potassium iodide), and iodine solution (2% iodine in water with sodium iodide) are currently official preparations in the USP. The iodide salt is admixed to increase the solubility of the iodine and to reduce its volatility. Iodine is one of the most effective and useful of the germicides. It probably acts to inactivate proteins by iodination of aromatic residues (phenylalanyl and tyrosyl) and oxidation (sulfhydryl groups). Mixing with several nonionic and cationic surfactants can solubilize iodine. Complexes form that retain the germicidal properties of the iodine while reducing its volatility and removing its irritant properties.12 In some of the more active, nonionic surfactant complexes, it is estimated that approximately 80% of the dissolved iodine remains available in bacteriologically active form. These active complexes, called iodophors, are both bactericidal and fungicidal.
Povidone-iodine (Betadine, Isodine, polymer polyvinylpyrrolidone [PVP]-iodine) is a charge-transfer complex of iodine with the nonionic surfactant PVP. The complex is extremely water soluble and releases iodine very slowly. Hence, the preparation provides a nontoxic, nonvolatile, and nonstaining form of iodine that is not irritating to the skin or to wounds. Approximately 10% of the iodine in the complex is bioavail-able. Povidone-iodine is used as an aqueous solution for presurgical disinfection of the incision site. It can also be used to treat infected wounds and damage to the skin, and it is effective for local bacterial and fungal infections. Several other forms of PVP-iodine are available, including aerosols, foams, ointments, surgical scrubs, antiseptic gauze pads, sponges, mouthwashes, and a preparation that disinfects whirlpool baths and hot tubs.
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