Exploring the Effects of Silver in Wound Management—What is Optimal?
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In recent years, use of silver in medical healthcare devices has seen a vast increase. This increase has been largely dominated by wound dressings. Silver sulfadiazine, which has been available for approximately 40 years, provides broad-spectrum antimicrobial activity and has been widely used, particularly as a topical cream to manage burn infection. In the last 5 years, the number of available silver-containing dressings has increased. These dressings are used primarily on chronic wounds and in clinical practice are regularly applied for periods of time up to and in excess of 4 weeks. As silver dressings may be used in clinical situations other than as a temporary option, it is important that potential toxicity be considered, particularly in relation to the type and amount of silver, and as regards the risk of selecting for bacterial resistance. These factors have been recently reviewed.1
This article will consider what happens once the body absorbs silver and discuss the levels of silver required to exert a toxic effect on bacteria. In addition, it will explore the relevance of the carrier dressing to efficacy of silver and the clinical relevance of microbial kill time. It is preferable that any testimony made in respect of silver should be clinically relevant. In order to do this, data should be drawn from clinical (in-vivo) studies wherever possible. Unfortunately, few such studies exist, so much data will be drawn from available in-vitro, ex-vivo, and animal studies.
Metabolic fate of topical silver. Silver, as a component of wound dressings, antibiotic cream, and first-aid plasters, comes into contact with intact skin and breached skin on an increasingly regular basis. The penchant for silver as an antimicrobial has seen it incorporated into simple adhesive dressings for minor cuts and abrasions and is no longer reserved for “serious” wound management. Potential repercussions associated with these applications need to be acknowledged and explored. Apart from increasing the risk of contact dermatitis and selecting for resistance, there will be concerns about possible systemic and cutaneous toxicity. The interaction of metallic silver with intact skin does not cause any detectable increase in blood levels and is not of great toxicological interest. However, the recent increase in the use of silver-based wound treatments raises some concerns about the systemic effects of silver and warrants a toxicological review. Several factors influence the capacity of a metal to produce either local or systemic toxic effects. These factors include 1) the degree of absorption as influenced by solubility of the metal or its compounds, 2) the ability to bind to biological sites, and 3) the degree to which the metal complexes are sequestered, metabolized, and ultimately excreted.
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