New silver dressings may serve critical role in your wound kit
Products provide more reliable methods of silver delivery to injured tissue
Silver has long been associated with the forces of good. Silver weapons were once believed to kill evil creatures. The Lone Ranger rode a horse named Silver and shot silver bullets at outlaws. And if a dark cloud holds hidden blessings, it is said to have a silver lining.
Many cultures around the world recognized the healing properties of silver centuries before the postulation of the germ theory and the identification of bacteria as a cause of infection. Today’s intractable infections have caused health care professionals to look once again toward silver to combat topical infections. The metal has proved itself a powerful bactericidal agent for burns, incisions, chronic wounds, and other diagnoses in which skin integrity has been violated.
For the past 2,500 years, silver has been a popular material for making drinking vessels, eating utensils, and surgical instruments, says Bart Flick, MD, an orthopedic surgeon in Lakemont, GA, who has investigated the use of silver in wound care for more than a decade. Once the nature and role of bacterial pathogens were accepted in the 19th century, silver’s stature in medicine grew when physicians discovered that the metal held bactericidal qualities. Silver nitrate was used successfully to treat skin ulcers, compound fractures, and suppurating wounds. In 1852, an Alabama surgeon pioneered the use of silver sutures during a procedure to repair a vesicovaginal fistula — an operation almost always accompanied by post-surgical infection in those days. In 1881, dilute silver nitrate was first dropped in the eyes of newborns to prevent gonorrheal ophthalmia.
Early in this century, a physician at Johns Hopkins Hospital reported the use of silver foil for dressing wounds, and even oral silver preparations were in vogue. But as highly effective antibiotics entered the medical armamentarium with a flourish, silver usage dropped precipitously.
But the ability of a growing number of bacteria to resist antibiotic therapy has led to an escalating battle between drug-resistant microorganisms and microbiologists attempting to develop new formulations to stop them. The antibiotic defense arsenal, once thought to be impenetrable, has been breached — and with potentially deadly consequences.
Microorganisms such as methicillin-resistant Staphylococcus aureus (MRSA), candida, and Escherichia coli frequently colonize wound sites. MRSA has been blamed by the Centers for Disease Control and Prevention for approximately 13% of the nation’s 2 million annual hospital-acquired infections.
Research has shown that silver’s antimicrobial endowment has been traced to silver ions that dissociate from the metal itself. So far, no bacterial pathogens have demonstrated a talent for surviving contact with ionized silver. In addition, no allergies to silver ions or metallic silver have been reported.
David Mitchell, PhD, director of research and development at Maersk Medical UK, writes: "Recent research has shown that silver in ionic dissociation is more effective than the silver itself, but this again suffers from rapid elimination. If small amounts of ionic silver can be constantly made available at the wound interface, then the efficacy of the antimicrobial action can be maintained. In addition, the amount of ionic silver required is very small indeed."1
Silver won’t cure but may prevent
Why not universally substitute silver for antibiotics? One reason is that there is no way to deliver silver ions systemically and nontoxically to infection sites; thus its application must be topical. Just as importantly, silver cannot be used to cure an existing infection, but it can prevent an incipient one or create an environment that greatly reduces the chances of infection. Another challenge of using silver, until recently, had been to find a way to deliver adequate levels of silver ions to tissue uniformly over extended periods.
Since the early 1970s, the common method of silver use for wound and burn care was via topical silver sulfadiazine cream. This product still provides clinicians with a straightforward modality for applying silver to burns and various types of wounds and is held in high esteem by many who use it regularly. Nowadays, clinicians often refer to silver sulfadiazine as Silvadene, regardless of the manufacturer, though Silvadene is actually a brand name. Several companies produce similar versions of the product.
Some users of silver sulfadiazine claim they have witnessed stunning wound-healing results after applying the cream to chronic wounds that were in danger of infection. Numerous studies of its use for a wide variety of diagnoses can be found in the literature, though specific investigations into its use on chronic wounds are scarce.
Yet even proponents of silver sulfadiazine admit it has some noteworthy drawbacks. Once applied to a wound, silver sulfadiazine actively discharges silver ions for a relatively short period of time, and those ions are quickly neutralized when they come into contact with body fluids. Therefore, the cream must be wiped away and replaced with a fresh batch two to three times daily in order to be effective. Secondary dressing changes must accompany the silver sulfadiazine reapplications, making the undertaking labor-intensive. The fact that reapplication is a messy job doesn’t add to its attractiveness. In addition, there is no way to measure the actual amount of silver ions that reach infected tissue.
Clinicians also should note that silver becomes toxic to the liver when present in high quantities, and because of the manner in which the cream is applied, it is impractical to expect consistent and accurate dosing. Because of the threat of toxicity, experts recommend that continuous application of silver sulfadiazine cease after two weeks. By that time, the silver should have killed the pathogens anyway.
A more reliable form of delivery
In recent years, a newer, more reliable method of delivering silver to burns, chronic wounds, surgical incisions, and other skin breaks (such as catheter insertion points) to prevent or decrease bacterial infections has been developed.
Several manufacturers have bonded silver to various dressing materials, with the result that silver ions are released steadily and for relatively long periods of time. This important development decreases the need for frequent dressing changes and the risk of silver toxicity and simultaneously guarantees that a therapeutic dose of silver reaches the wound and effectively reduces the bioburden. Theoretically, faster healing should follow.
Two silver-impregnated dressings are currently on the market: Arglaes, manufactured by Maersk Medical UK and distributed in the United States by Medline Industries of Mundelein, IL, and Acticoat, manufactured by Westaim Corp., Fort Saskatchewan, Canada. A third silver dressing, Silverlon, manufactured by Argentum International LLC of Providence, RI, has received Food and Drug Administration marketing approval and is expected to enter the market this winter.
Before its approval in the United States, Arglaes had been used in Great Britain for several years. Acticoat, while initially developed for the burn market, is being used more frequently for chronic wound patients.
Reference
1. Mitchell D. Wound care beyond 2000 (abstract). Presented at the Symposium on Advanced Wound Care & 8th Annual Medical Research Forum on Wound Repair. Miami Beach, FL; April 18-22, 1997.
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