I have to admit, when I first heard that more medical and surgical supplies are sporting silver coatings, I was skeptical as to whether they would provide any real benefits. Blame it on my cynical nature, or the fact that the notion of silver as an effective antimicrobial agent has been discussed for centuries, making it seem a bit like superstition to me.

The use of silver to control infections and spoilage was quite widespread in ancient civilizations such as Greece, Rome, Phoenicia and Macedonia. Serious scientific study on the topic began at the turn of the 20th century: An Annals of Surgery article from 1909 analyzes the value of silver foil as a surgical dressing, citing research from 1899 and 1893.1

But modern research indicates that silver, when formulated correctly, does present infection prevention abilities. The key, apparently, is the amount of silver used: Too little or too much is ineffective.

Heavy metal Large doses administered over a prolonged period of time could be harmful, but the formulations for commercial products containing silver are a far cry from those levels. Further, the silver companies are using for Foley catheters, in-dwelling catheter tubes, surgical site dressings and even some implants is not metallic silver but engineered silver oxide.

Unlike a lot of metals, silver is usually harmless to the body - especially in the tiny amounts we're talking about here. Humans actually take in about 80?m of the metal every day. And unlike other heavy metals such as mercury and lead, which will build up in the body due to their chemistry, and inhibit metabolism, silver is readily excreted, making it non-toxic in small doses and safe for use in a post-op wound dressing.2 The manufacturing processes have managed to maintain this inert quality of silver while capitalizing on its infection-fighting abilities.

In your pocket In doing a literature search, I found that the recent research on these formulations is mostly positive, both from an infection and cost perspective:

• One hospital decided as a result of its research that silver-coated catheters reduced healthcare-acquired UTIs more than its previous efforts and estimated its annual net cost savings - based on infection cost and the increased cost of the catheter - at $16,628.3
• Over two months of silver-coated catheter use, the University of Virginia Health Sciences Center saw between a 35 and 39 percent decrease in the rate of patients developing UTIs, while patients with uncoated catheters actually had a higher incidence of infection.4
• Finally, another facility found that it decreased healthcare-acquired UTIs by 56.6 percent by using silver/hydrogel-coated Foley catheters. Even better, it estimated cost savings during the six-month trial period to be $24,330.5

When you consider that surgical site infections result in an average patient stay of 14.5 days and an average charge of $132,110 (according to the recent and extensive report out of Pennsylvania), the savings could be even greater when you apply the technology to post-surgical wound care.6

Here's a look at some such efficacy studies.

• One study looked at three types of silver applications for wounds - silver nitrate liquid, silver sulfadiazine cream and silver-coated dressings - and found that all reduced the number of viable bacteria, though efficacy against antibiotic-resistant bacteria varied. Against those, the dressings were the most effective and the liquid the least. Researchers concluded that silver might be useful for preventing "wound colonization by organisms that impeded healing."7
• Another study that specifically sought to compare the efficacy of silver-coated wound dressing against other methods (the aforementioned cream and liquid, as well as mafenide acetate, also known as the topical antibiotic Sulfamylon) found that the dressing outperformed the liquid and cream.

The mafenide acetate showed the broader kill, but the silver-coated dressing had the lowest minimum inhibitory concentrations and lowest minimum bactericidal concentrations - viable bacteria were undetectable after 30 minutes, whereas a significant number of bacteria still survived six hours after treatment with the mafenide acetate.8

The second study was done using burn patients, as is a lot of the research in this area, but the principles transfer.

A silver bullet? When you consider that many SSIs are the result of pathogens that enter through a wound and that are resistant to antibodies, silver becomes more attractive for use. Because it has wide-spectrum infection-fighting capabilities and is applied on the surface, you may be able to decrease antibiotic use while maintaining or improving upon your SSI rates. There isn't yet enough evidence to say that you should entirely change your infection prophylaxis, but it may at least merit a trial.

References
1. Lewis JS. "Note on Silver Foil in Surgery." Ann Surg. 1909 October; 50(4): 793?796. Accessed 2 Oct. 2006. writeOutLink("www.pubmedcentral.nih.gov/pagerender.fcgi?artid=1407167&pageindex=1",1)
2. Tobbler D, Warner L. "Nanotech Silver Fights Microbes in Medical Devices." Medical Device and Diagnostic Industry. May 2005. writeOutLink("www.devicelink.com/mddi/archive/05/05/029.html",1) 1 Dec. 2006.
3. Lee J, Hernandez J. "Silver/Hydrogel-coated Foley Catheter Used to Reduce Incidence of Nosocomial Urinary Tract Infections." Am J Infect Control 1996;24:2:117
4. Karchmer TB, et al. "Randomized Cross-Over Study of Silver-Coated Urinary Catheters in Hospitalized Patients." Arch Intern Med. 2000;160:3294-3298.
5. White E, Jones D. "Does the Silver/Hydrogel-coated Foley Catheter Really Make a Difference?" Am J Infect Control 1997;25:2:168.
6. "Hospital-acquired Infections in Pennsylvania 2005." Pennsylvania Health Care Cost Containment Council. Nov. 2006. writeOutLink("www.phc4.org/reports/hai/05",1) 1 Dec. 2006.
7. Wright JB, Lam K, and Burrell RE. "Wound Management in an Era of Increasing Bacterial Antibiotic Resistance: A Role for Topical Silver Treatment." Am J Infect Control 1998:26:572-7.
8. Yin HQ, Langford R, Burrell RE. "Comparative Evaluation of the Antimicrobial Activity of Acticoat Antimicrobial Barrier Dressing." J Burn Care Rehab 1999;20:195-200.