Antimicrobial Wound Dressings – Silver

The use of silver in wound care has a long history. A recent resurgence in interest in silver dressings as antiseptic agents has come about, largely due to an increase in antimicrobial-resistant organisms such as MRSA (methicillin-resistant staphylococcus aureus).

What is silver’s mechanism of action?

Silver is effective as an antimicrobial because it binds to and destroys bacteria cells at multiple sites. This ability to bind to several sites is the main reason why bacterial resistance to silver is rare, making silver an attractive option.

When the silver cation binds to proteins in the bacteria, the following can result:

– The protein structure is altered, causing structural and functional changes in the cell

– The bacterial cell wall can rupture, causing its contents to leak out, leading to cell death

– The bacteria is prevented from carrying out functions necessary for its survival, such as respiration and taking in nutrients, leading to cell death

Antibiotics usually only have one method of killing bacteria (i.e. preventing replication) while silver has several methods of killing bacteria.

What types of silver dressings are available?

Silver dressings are commercially available in several forms. The main difference in these dressings is in how much silver they contain and how quickly they release the silver cation. At present silver dressings are found in the following forms:

– Films

– Foams

– Alginates

– Hydrogels

– Hydrocolloids

The form in which you choose to deliver silver to the wound will depend on the type of wound, where it is located, and the amount of drainage present.

When should I use silver?

Dressings containing silver may be appropriate for short-term use on wounds that are critically colonized or infected. You should be cautious about using silver for wounds that show signs of cellulitis or a systemic infection, wounds that are colonized with fungus, in clients with interstitial nephritis or leucopoenia, and when signs of possible side effects are present, such as erythema multiforme. Silver should not be used solely to treat an infection, but as an adjunct to help decrease the number of bacteria on the surface of a wound. Keep in mind that using more silver is not necessarily better, as silver has been found to be cytotoxic to fibroblasts and single layers of epithelial cells in vitro as well and retards wound epithelialization in vivo. Use dressings with the least amount of silver necessary to get the job done.

Note that there are two substances that should not be used in conjunction with silver:

Saline – Saline will react with the silver cation to form silver chloride crystals, consequently decreasing the amount of silver released. This is important to know, as many times saline is used as a cleansing agent during dressing changes.

Papain-urea deriding ointment – The ointment will be deactivated by the silver, thus rendering it useless as a debriding agent.

In addition, silver dressings must be removed if a patient is to undergo an MRI. They should be discontinued once wound bioburden is controlled and wound healing progresses. Silver dressings should also be discontinued, and alternate treatments initiated, if no improvements in wound status are noted after 1 or 2 weeks of use.

Silver is making a comeback as a treatment option to help decrease bacterial loads in wounds. Although it has many advantages, silver also has its drawbacks.