Words on Wounds

A forum to discuss the latest news and ideas in skin and wound care.

Monday, September 10, 2012

Silver Versus Iodine

According to results of our quick poll on silver versus iodine, silver was voted as a more effective agent against biofilm than iodine. This is an interesting debate. It is important to remember that silver is an inert metal that exerts antimicrobial effective against microorganisms only when it is converted by oxidation to the ionic form. Ionization of silver requires a wet environment that may not be ideal for wounds that produce very minimal exudate or wounds that are intended to kept dry due to poor healing potential.

Indeed, the use of povidone-iodine PVP-I in wound healing is controversial in light of its cytotoxicity. Betadine is one of the most extensively used board-spectrum topical antiseptics that consists of 10% PVP-I in an aqueous solution. As an iodophor, PVP-I is produced by attaching free iodine to the carrier pyrrolidone, a water-soluble polymer of high colloidal and osmotic pressure. Free iodine that is released from the PVP molecules exerts its antimicrobial property by combining irreversibly with tyrosine residues of proteins, disrupting the formation of hydrogen bonding in amino acids and nucleotides, oxidizing sulfhydryl (-SH) groups that are essential building blocks of many proteins including important enzymes, and reacting with sites of unsaturated fatty acids.

In vitro, PVP-I has been demonstrated to be active against a board spectrum of pathogens, including gram-positive (such as methicillin-resistant Staphylococcus aureus) and gram-negative bacteria, spores forming fungi, protozoa, and viruses. A number of studies and meta-analysis indicate that PVP-I may not be as cytotoxic as we thought it was. The activity of PVP-I is neutralized in the presence of blood, fats, pus, and serum protein commonly found in the wound milieu. Up to 80% of free iodine can bind to plasma protein, rendering betadine less damaging to the wound. The more copious amount of fluid exudes from the wound, the less iodine is available to interact with healthy cells. Although the paper has not been published yet, there is preliminary data to suggest that iodine is more effective in penetrating into biofilm to destroy bacteria. In addition, the desiccating effect of PVP-I may interrupt the glycocalyx and destroy biofilm structures. Further study is required to compare silver to betadine.