Comment on: The increasing use of silver-based products as antimicrobial agents: a useful development or a cause for concern?

Sir, We read the article by Chopra on the increasing use of silverbased products with interest and we would like to make some observations. The title of the article asked whether there was cause for concern, and, understandably, the issue of resistance was raised in this respect. Chopra makes a case for using dressings that release high concentrations of silver in order to overcome this, yet, in certain circumstances, this could raise the possibility of toxicity. Silver-processed products range from wound dressings to catheters, and the individual exposure to silver will vary enormously. Systemic toxicity (argyria) is rare but has been reported after topical use. Although reports of actual morbidity due to argyria are rare, neuropathy has been reported from topical use and from the use of silver in bone cement. Of equal concern is the selective deposition of silver in the CNS – 7 associated with the use of intracranial catheters, two of which are now available (Silverline, Spiegelberg GmbH; Vygon Expert, Vygon GmbH). In addition, local cytotoxicity has been demonstrated when silver-coated implants have been evaluated. It appears that the window between minimum concentrations lethal to microbes and those lethal to host cells is narrow and is easily missed in practice. In most cases this will not be clinically important, but in some it will be. The design of the silver release system is also important. For example, if the aim is to kill microbes that impinge on the device, such as in a catheter, then low rates of release of silver ions from perhaps a nanoparticle system might suffice, but if the effect of silver is to be exerted in the surrounding tissue or exudates, as in a dressing, then greater amounts of silver must be released and this might be best in the form of a silver salt. Finally, Chopra discussed the zones of inhibition expected from silver systems, yet one would not see a zone of inhibition from a nanoparticle system despite its ability to kill attached microbes, but one might with a silver salt system. The diversity of silver systems available and the often inadequate understanding of their modes of action have in our view led to confusion over the clinical efficacy of silver. Chopra’s article is timely in that it raises the issue and hopefully will stimulate debate.