The element iodine was discovered in 1811 and was tried as a wound treatment for many years, principally during the American
Civil War. In its elemental form, it inhibited bacteria but also caused pain, skin irritation and discoloration. The development
of iodophors—mixtures of polyvinyl surfactant iodine complexes such as povidone-iodine—in the late 1940s made this agent safer,
less painful and more effective. Iodophors release low-level concentrations of free iodine that produce multiple cellular
effects by binding to proteins, nucleotides and fatty acids to block hydrogen bonding. Povidone-iodine has broad-spectrum
activity against microbes, including bacteria, mycobacteria, fungi, protozoa and viruses.
"Its efficacy as a skin disinfectant is undisputed," says Cooper. "And numerous publications describe the use of iodine in
cleansing wounds and as a topical agent to prevent or treat localized wound infections."
Some controversy exists regarding the use of povidone-iodine. Severe metabolic acidosis has been reported after use, and although
these are isolated cases with questionable methodology, there's still a strong view in human medicine that povidone-iodine
use should be restricted to brief topical application on superficial wounds, rather than long-term use on large wounds. Clearly,
more research should be done in this area to increase confidence concerning iodophore use and to possibly clear the path for
increased application of this treatment agent.
Of all the older antimicrobial agents enjoying renewed interest, perhaps the one with the most tremendous potential is silver.
Colloidal silver is effective against bacteria in extremely low concentrations. Studies have shown 0.01 to 0.04 ppm to be
effective against hundreds of types of bacteria and 3 to 5 ppm to be effective against nearly 650 different microbes.
Colloidal silver is a solution in which microscopic, electrically charged particles of silver are in suspension. Electrolysis
of very pure water (less than 1 ppm of contamination) using a 99.9 percent pure silver electrode places a positive charge
on silver ions and places them in solution.
The quality of the water and the silver are crucial to the production of a functional product, as is the strict control of
current flow. Tap water contains roughly 100 to 300 ppm of dissolved solids, so highly distilled or deionized water must be
used, but the resultant product has tremendous potential to provide veterinarians with antimicrobial agents that can take
on the resistant bacteria and viruses we're increasingly encountering.
"Silver ions avidly bind to negatively charged components in proteins and nucleic acids, thereby effecting structural changes
in bacterial components in proteins and in nucleic acids that affect viability," says Cooper. She adds that silver ions cause
multiple deleterious events in microbes rather than specific lesions, making colloidal silver much more destructive to bacteria
and viruses and much harder for pathogenic organisms to develop resistance to.
Multiple research projects have shown silver sulfadiazine (SSD) to possess broad-spectrum antibacterial, antifungal and antiviral
activity. Hanson notes, "SSD's antibacterial activity includes Pseudomonas species, and contrary to what has been noted in other species, it does not decrease the rate of wound contracture in horses."
Many silver-based wound treatment products are coming into the veterinary marketplace, and there likely will be more as ongoing
silver research continues to show promise.
A new company, EquiSilver, has begun using chelated silver rather than colloidal silver in an attempt to get even greater
cellular penetration and antimicrobial action. This agent features a chelator bound tightly to a metal atom (silver in this
case, but many minerals are commonly chelated), which forces the metal atom to go wherever the chelator goes. This combination
of chelator and metal atom is called a chelate. Chelators are intended to carry atoms into the body in higher concentrations than normally would be allowed. It's proposed
that the chelator is treated as a desirable molecule by the recognition system in cell walls and, consequently, the chelate
is allowed entry. Research at the College of Veterinary Medicine at the University of Florida and elsewhere is underway looking
at the beneficial effects of chelated silver on topical wounds but also on internal conditions of the guttural pouch, pharynx,
larynx and lungs in horses.