Whether it is used as a topical ingredient or a dressing ingredient, the use of silver in treating wounds has been around for quite some time. Silver has an array of beneficial effects in promoting healing. Given the potential of silver in the wound care arena, our expert panelists take a closer look at the history of silver in wound care, key indications and their experience with the different modalities that contain silver.
Q: Historically, how has topical silver been used in wound care?
A: The panelists note that silver has been recognized for centuries as a useful antimicrobial agent.
In the early 19th century, surgeons used silver sutures to close incisions in surgeries (such as the repair of vesico-vaginal fistulas) that were known to commonly result in postoperative infections, according to Liza G. Ovington, PhD, CWS. She adds that diluted (1 to 2%) silver nitrate solutions were used commonly to treat gonorrhea.
William Ennis, DO, MBA, Jason Weber, DPM, and Dr. Ovington also note that silver nitrate was used to prevent and/or treat eye infections in newborn babies.
Drs. Ovington and Weber point out that thin sheets of silver foil were employed to cover open wounds as well as surgical wounds. While the advent of antibiotics such as penicillin in the 1930s led to a decline in the use of silver products as antimicrobials, all of the panelists note that silver, specifically silver sulfadiazine, has been commonly used as an antiseptic to help treat burn wounds since the 1960s.
In addition, physicians use silver-coated catheters for their slow-release antiseptic activities, according to Dr. Ovington. There has also been a recent resurgence in employing topical silver in wound care. Dr. Ovington and Alan Cantor, DPM, CWS, say the advent of new sustained release delivery systems have made it possible for silver to be incorporated into a wide variety of dressing materials.
Q: How do silver impregnated products promote wound healing and decrease infection?
A: Dr. Ennis says silver has broad spectrum antimicrobial properties against a wide spectrum of gram-positive and gram-negative bacteria. By controlling the bioburden, silver facilitates less competition for nutrients and less production of toxic metabolites, according to Dr. Ennis.
Dr. Cantor notes ionic silver, which is a key ingredient in modern wound dressings, promotes healing by facilitating the following:
• decrease of matrix metalloproteinase (MMP) activity;
• blocking of the respiratory cycle of bacterial cell wall membrane;
• decrease of excessive neutrophil response;
• regulation of inflammatory response without shutting off essential pro-healing functions; and
• increase of surface levels of calcium.
In other words, Dr. Ovington explains that silver impregnated products, which provide a sustained release of positively charged silver ions at the wound surface, can promote wound healing and decrease infection by killing bacteria. She adds that a decrease in bacterial numbers at the wound surface can result in fewer bacteria invading the deeper tissue compartment as well as decreased amounts of bacterially derived chemicals such as proteases and toxins that interfere with wound healing from a biochemical standpoint.
Dr. Weber says silver ions exhibit their antimicrobial effect by “avidly binding” to negatively charged components in proteins and nucleic acids, thereby affecting structural changes in bacterial cell walls, membranes and other products that are believed to affect the viability of the organism. Specifically, he notes researchers believe silver ions interact with thiol groups, phosphates, indoles, imidazoles, carboxylates, amines and hydroxyls.
In particular, the silver cation Ag+ is a “very potent antimicrobial agent because it can attack and damage bacterial cells at multiple sites,” notes Dr. Ovington. She explains that it attaches to specific chemical groups (thiol groups containing sulfur and hydrogen) found on a wide variety of proteins that play structural and functional roles in the bacterial cell.
Once Ag+ attaches to these sites, Dr. Ovington says the cation causes structural and functional changes in the cell. For example, she notes that when Ag+ binds to proteins in the cell membrane, the cell wall can rupture and leak, resulting in the death of the bacterial cell.
Dr. Ovington emphasizes that researchers have shown the silver ions are bactericidal against nearly 150 strains of bacteria as well as common fungi.
A: Dr. Ennis primarily uses impregnated alginates and foams. Dr. Cantor praises the foam-backed, ionic silver product Algidex Ag for its “excellent absorption” and notes that it is particularly effective on heel wounds due to the foam cushion and silver delivery.
Dr. Cantor cites Acticoat (Smith & Nephew) as being “instrumental” in facilitating the rise of silver-impregnated dressings in the late 1990s. Acticoat facilitates healing by depositing nanocrystals on the wound surface, but Dr. Cantor cautions that one may see temporary staining of the skin, which can interfere with assessing the wound bed, especially when clinicians are evaluating patients who have darker pigmentation.
Employing silver alginates like Acticoat and Silvercel (Johnson & Johnson), the silver hydrofiber Aquacel Ag (ConvaTec) or the silver foam Contreet F (Coloplast) can be helpful in managing highly exuding ulcers, according to Dr. Ovington.
Dr. Cantor concurs, emphasizing that the structural makeup of Aquacel Ag immobilizes both exudate and microrganisms within the structural makeup of the hydrofibers. He says the modality also reduces seepage and periwound maceration. In regard to Silvercel, Dr. Cantor says it provides “excellent absorption” for exuding wounds.
When it comes to low exuding wounds, Dr. Ovington says the silver hydrocolloid Contreet H (Coloplast) and the silver hydrogel Silvasorb (Medline) are useful in maintaining tissue hydration while controlling bacteria.
Q: Are there any contraindications for these products?
A: Dr. Ovington says most topical wound dressings are contraindicated for third-degree burns. Drs. Ennis and Weber suggest extra caution when considering silver products for patients who have a history of metal allergy. While silver allergies or hypersensitivities are rare, Dr. Weber notes they do affect a percentage of the population.
Dr. Ovington emphasizes that clinicians should use exercise caution when using silver products in the presence of enzymatic debriding agents. “Metal ions such as silver are known to inactivate enzymes and may negate the debriding effect,” explains Dr. Ovington.
The majority of the panelists cite the possibility of staining of the skin in and around the wound due to the use of silver in the tissues. While Dr. Ovington says this is “primarily a cosmetic problem,” she says it may indicate that very high amounts of silver are being released at the wound surface. This can potentially delay epithelialization, cautions Dr. Ovington.
Dr. Weber adds this discoloration and irritation is well documented but mainly occurs with silver nitrate. However, he notes some have observed absorption of silver, systemic distribution of silver and excretion of silver in urine among patients who have used topical silver products. When it comes to using silver nitrate and silver sulfadiazine (SSD), Dr. Weber adds there have been rare cases of leucopenia, bone marrow toxicity as well as renal and hepatic damage through silver deposition.
Dr. Ovington notes the leucopenia associated with SSD is transient and reverses after the SSD has been discontinued.
The presence of silver is contraindicated if you are considering the use of electrical stimulation for a patient, according to Dr. Ennis.
Q: Are there any pearls you would recommend when using silver dressings on wounds?
A: While only a small number of silver ions are required at the wound site, Dr. Weber notes that ionic silver suffers from rapid elimination. Therefore, he says it is important for clinicians to follow manufacturers’ guidelines on the frequency of dressing changes as different dressings release the ions at different rates.
However, Dr. Ovington points out that all silver dressings release the same active ingredient, namely the silver cation. While different dressings may release different amounts of silver ions or release the ions at different rates, Dr. Ovington says there is no clinical data to suggest these differences result in clinical outcomes.
Given this, Dr. Ovington says one should select a particular silver dressing based on additional benefits beyond its antimicrobial effect. These additional benefits may include the dressing’s ability to absorb exudate, its ability to provide wound hydration, adherence qualities or conformity.
All the panelists agree that one should choose the dressing that is most appropriate for the needs of the patient. For example, Dr. Ennis notes that if a patient will have his or her dressing changed only once a week, then a seven-day wear formulation makes sense. However, if the patient is undergoing daily pulse lavage, Dr. Ennis says one may want to postpone the use of silver technology until the pulse lavage has been discontinued.
Dr. Cantor cautions against leaving the silver dressings on too long. Even if a dressing is advertised as a seven-day dressing, he suggests doing a quick dressing inspection to verify the absence of seepage or corrosive maceration just to make certain the dressing will remain in place for a full seven-day course.
Noting that silver ions not only kill bacterial cells but can also kill host cells, Dr. Ovington warns against using silver dressings for long periods of time. She points out that using topical silver for longer than two to three weeks may increase the chance of cytotoxicity to host cells.
Dr. Cantor is an Attending Surgeon in the Burn and Wound Center at the Nassau University Medical Center in East Meadow, N.Y. He is an Attending Surgeon and Wound Management Consultant at Saint Mary’s Hospital for Children in Bayside, New York. Dr. Cantor is also a faculty member of the Oxford University Wound Healing Institute in the United Kingdom.
Dr. Ennis is the Medical Director of the Wound Treatment Program and Fellowship Program at Advocate Christ Medical Center in Oak Lawn, Ill.
Dr. Ovington is the President of Ovington & Associates, Inc., a wound care consulting company in Allentown, Pa. She is an Adjunct Faculty Member in the Department of Dermatology and Cutaneous Surgery at the University of Miami School of Medicine.
Dr. Karlock (pictured) is a Fellow of the American College of Foot and Ankle Surgeons and practices in Austintown, Ohio. He is a member of the Editorial Advisory Board for WOUNDS, a Compendium of Clinical Research and Practice.