Given the increasing prevalence of antimicrobial resistance, there is a growing interest in emerging wound care products that contain silver. Topical silver has a broad range of antimicrobial activity and has been used extensively to help treat high-risk burn patients. Research has confirmed that silver is effective against gram negative and positive bacteria, methicillin resistant Staph aureus (MRSA), yeast, filamentous fungi and viruses (including varicella zoster and herpes simplex types I and II).1-4 Interestingly, the use of silver for medicinal purposes has been documented back to the time of the Roman empire.5 However, it was not until the late 1800s that silver was documented as being bactericidal. In 1881, Carl Crede, MD, pioneered the installation of dilute silver nitrate in the eyes of neonates to prevent gonorrheal ophthalmia. In fact, the technique still has use today.4,5 William Halstead, MD, a founding father of modern surgery, promoted the use of silver foil dressings for wounds.5 Clinicians used these types of dressings at length until after World War II and they were listed in the Physician’s Desk Reference until 1955. As late as the 1970s, Becker, Marino and Spadaro of the Syracuse, N.Y. Veterans Affairs Hospital, performed studies on the treatment of bone infections with silver-coated fabrics.5 A Closer Look At The Impact And Re-Emergence Of Silver In Wound Care Silver (Ag) is the 47th element in the periodic table of elements. In order for silver to have antimicrobial properties, it must be in its cation form, Ag+. This cation has the ability to bind at multiple sites on bacterial cells (such as bacterial DNA, bacterial enzymes and to proteins in the cell wall), causing cell death and destruction. The silver cation will bind to thiol groups containing sulfur and hydrogen on important proteins that play structural and functional roles to the bacterial cell.2 The medical industry is capitalizing on the healing potential of silver and has been actively developing new products containing silver. There seems to be a new silver containing wound product or dressing every day. Silver is being incorporated into wound vacuum sponges, various topical formulations and a wide array of wound care products. Certainly, clinicians can utilize these new products to help heal difficult wounds. However, questions abound about which product is best, how much silver is needed and when one should use a silver-containing product. Common delivery vehicles include foams, alginates, films, sheets and hydrocolloids. There are also a number of available technologies that release various concentrations of silver cations to wounds. These technologies include silver salts, absorbed or trapped ionic silver in silver charcoal metallic silver products, and nanocrystalline silver coatings that use silver vapor sprayed onto the backings of dressing materials.1 What The Research Says About The Efficacy Of Silver In deciding what specific topical silver to use in a particular clinical situation, one has to identify the differences in rate, amount and delivery of the silver cation to the wound bed. Unfortunately, most of the current literature demonstrates only the in vitro comparisons of silver dressings to specific organisms as opposed to comparisons in actual in vivo environments.2,4,6 Thomas and McCubbin compared antimicrobial effects of four silver-containing dressings on three organisms.4 In this study, they found Acticoat (Smith & Nephew) has a much more rapid onset of action and better performance than the other three products.4 Most of the other products tested still had antimicrobial effects. However, they did not have as a rapid of an effect as Acticoat. Another study by Ovington examined the rate of silver cation release and whether a faster rate was more clinically significant than a slower rate of cation release.2 Of all the dressings tested, each achieved the same reduction in bacterial counts within two hours. This is still less than the typical timeframe between dressing changes.2 Other studies have discussed the amount of silver in dressings and whether too much silver in the wound bed would be harmful to wound healing. It seems that the amount of silver in a particular product is not as important as the amount and rate of silver cations released to the wound bed. In wounds with low bacterial counts, Poon and Burd noted that high silver cation-releasing products can actually bind to the fibroblasts and epithelial host cells, causing delayed wound healing.7 Innes, et. al., studied the effects of silver on wounds with low bacterial counts and found a delay in epithelialized wounds such as skin graft donor sites.3 The authors compared Acticoat versus absorbent polyurethane foam on skin graft donor sites (a clean, superficial and epithelializing wound bed). These findings did not support the use of Acticoat as a skin graft donor site dressing. Other Pertinent Pointers On Using Silver Products Although some studies show the deleterious effects of silver on wounds, the impact of silver depends on not only the type of wound bed but also the amount of silver that is being released in the wound. For example, in an infected deep wound, one would need to utilize a silver product with a large amount of silver cation release compared to a clean superficial wound with fragile neo-epithelialization. In regard to the delivery of silver in wounds, Thomas and McCubbin found that Contreet H (Coloplast) was effective after an extended period of time due to the fact that it is a hydrocolloid. This product contains an undisclosed silver complex that is activated by the uptake of wound fluid.4 This illustrates the importance of proper use of wound care products in specific wound types. The dressing vehicle is mainly dependent on the wound bed’s characteristics. For example, one should not use a silver impregnated alginate dressing on a dry, non-exudative wound. The dressing delivery mechanism will affect the overall performance of the product in terms of its ability to control moisture maintenance or exudate management in the wound.2 There are some important considerations when clinicians are looking to apply these silver dressings on wounds. For example, the product information guides for Acticoat and Silverlon (Argentum Medical) state that one should use sterile water (not saline) on their respective products. The chloride ion in normal saline reacts with the pure metallic silver coating of the Silverlon product to form silver chloride crystals, reducing the release of ionic silver (Ag+, the form necessary for the antimicrobial properties of silver).8 Smith and Nephew reinforces this same concept with Acticoat.9 In addition, the company also suggests not using papain-urea debriding agents, which tend to be inactivated by the silver salts of the Acticoat.10 Driver discusses these points in presenting the clinical role of silver dressings.1 In Conclusion Silver dressings do not “cure” infections. However, when clinicians employ these dressings proactively, they can inhibit the progression of bacterial penetration and be effective against MRSA and most other superficial wound pathogens.1 There is a great benefit to the proper utilization of silver products in the hospital setting, especially between surgical debridements. The use of antimicrobial prophylaxis is important in reducing the wound’s microbial load as it can help facilitate wound healing.7 For example, patients who are surgically unstable or awaiting their next debridement would be excellent candidates for the use of silver products in their respective wound beds. Dr. Friedman is a PGY-II resident at the Washington Hospital Center in Washington, D.C. Dr. Bass is a PGY-III resident at the Washington Hospital Center in Washington, D.C. Dr. Steinberg (pictured) is an Assistant Professor in the Department of Plastic Surgery at the Georgetown University School of Medicine in Washington, D.C. For related articles, see “What You Should Know About Using Silver Products In Wound Care” in the November 2004 issue of Podiatry Today.
References 1. Driver VR. Silver Dressings in Clinical Practice. Ostomy/Wound Management 2004;50(9A suppl): 11S-15S. 2. Ovington LG. The Truth about Silver. Ostomy/Wound Management 2004;50(9A suppl): 1S-10S. 3. Innes ME, Umraw N, Fish JS, Gomez M, Cartotto RC. The use of silver coated dressings on donor site wounds: a prospective, controlled matched pair study. Burns. 2001;6):621-627. 4. Thomas S, McCubbin P. A Comparison of the antimicrobial effects of four silver-containing dressings on three organisms. Journal of Wound Care. 2003; 12:3, 101-107. 5. http://www.silverlon.com/history.html . Accessed January 11, 2006. 6. Wright J, Lam K, Burrell R. Wound Management in an era of increasing bacterial antibiotic resistance: A role for topical silver treatment. American Journal of Infection Control. 1998; Vol 26:6 572-577. 7. Poon VKM, Burd P. In vitro cytotoxicity of silver: implications for clinical wound care. Burns. 2004;30:140-147. 8. Argentum Medical, LLC: Silverlon FAQs. Available at: http://www.silverlon.com/faq.htm Accessed January 11, 2006. 9. Smith and Nephew:Acticoat* 7, Acticoat* Absorbent, Acticoat* Burn. Available at: http://wound.smith nephew.com/us/Standard.asp?NodeId=2592 . Accessed January 11, 2006. 10. Smith and Nephew:Glidase:papain-urea debriding ointment. Available at: http://wound.smith-nephew.com/us/node.asp?NodeID=2927 . Accessed January 11, 2006.