The medical uses of silver include its use in wound dressings, creams, and as an antibiotic coating on medical devices. Wound dressings containing silver sulfadiazine or silver nanomaterials may be used to treat external infections. The limited evidence available shows that silver coatings on endotracheal breathing tubes may reduce the incidence of ventilator-associated pneumonia. There is tentative evidence that using silver-alloy indwelling catheters for short-term catheterizing will reduce the risk of catheter-acquired urinary tract infections.
Silver generally has low toxicity, and minimal risk is expected when silver is used in approved medical applications. Alternative medicine products such as colloidal silver are not safe or effective.
Mechanism of action
Silver and most silver compounds have an oligodynamic effect and are toxic for bacteria, algae, and fungi in vitro. The antibacterial action of silver is dependent on the silver ion. The effectiveness of silver compounds as an antiseptic is based on the ability of the biologically active silver ion () to irreversibly damage key enzyme systems in the cell membranes of pathogens. The antibacterial action of silver has long been known to be enhanced by the presence of an electric field. Applying an electric current across silver electrodes enhances antibiotic action at the anode, likely due to the release of silver into the bacterial culture. The antibacterial action of electrodes coated with silver nanostructures is greatly improved in the presence of an electric field.
Silver, used as a topical antiseptic, is incorporated by bacteria it kills. Thus dead bacteria may be the source of silver that may kill additional bacteria.
Medical uses
Antibacterial cream
Silver sulfadiazine (SSD) is a topical antibiotic used in partial thickness and full thickness burns to prevent infection. It was discovered in the 1960s, and was the standard topical antimicrobial for burn wounds for decades.
However systemic reviews in 2014, 2017 and 2018 concluded that more modern treatments, both with and without silver, show better results for wound healing and infection-prevention than silver sulfadiazine, and therefore SSD is no longer generally recommended.
It is on the World Health Organization's List of Essential Medicines. The US Food and Drug Administration (FDA) approved a number of topical preparations of silver sulfadiazine for treatment of second-degree and third-degree burns.
Dressings
Despite its widespread use, there is only mixed evidence that silver in dressings has any benefit. A 2018 Cochrane review found that silver-containing dressings may increase the probability of healing for venous leg ulcers.
A number of wound dressings containing silver as an anti-bacterial have been cleared by the U.S. Food and Drug Administration (FDA). However, silver-containing dressings may cause staining, and in some cases tingling sensations as well.
Endotracheal tubes
A 2015 systematic review concluded that the limited evidence available indicates that using silver-coated endotracheal breathing tubes reduces the risk of contracting ventilator-associated pneumonia (VAP), especially during the initial days of utilisation. A 2014 study concluded that using silver-coated endotracheal tubes will help to prevent VAP and that this may save on hospital costs. A 2012 systematic review of randomized controlled trials concluded that the limited evidence available indicates that using silver-coated endotracheal tubes will reduce the incidence of ventilator-associated pneumonia, microbiologic burden, and device-related adverse events among adult patients. Another 2012 review agreed that the use of silver-coated endotracheal tubes reduces the prevalence of VAP in intubated patients, but cautioned that this on its own is not sufficient to prevent infection. They also suggested that more research is needed to establish the cost-effectiveness of the treatment. Another 2012 study agreed that there is evidence that endotracheal tubes coated with silver may reduce the incidence of ventilator associated pneumonia (VAP) and delay its onset, but concluded that no benefit was seen in the duration of intubation, the duration of stay in intensive care or the mortality rate. They also raised concerns surrounding the unblinded nature of some of the studies then available.
The U.S. Food and Drug Administration in 2007 cleared an endotracheal tube with a fine coat of silver to reduce the risk of ventilator-associated pneumonia.