Metals as Antiseptics and Disinfectants
Inorganic mercuric bichloride, one of the early antiseptics, was later replaced by the less irritant and less toxic organic mercurials, eg, merbromin, thimerosal (49% mercury), nitromersol, and phenylmercuric nitrate. At moderate concentrations, the organic mercurials are bacteriostatic and act by inhibiting bacterial enzymes through their affinity for sulfhydryl groups. This effect can be reversed by sulfur-containing compounds, eg, cysteine or glutathione. Mercurials are not effective against spores. Use of mercurial antiseptics or disinfectants has decreased, partly because of their environmental persistence and contaminant potential. Repeated application of topical mercurials can result in significant absorption and systemic toxicity.
Silver compounds can have caustic, astringent, and antibacterial effects. Silver ions combine with sulfhydryl, amino, phosphate, and carboxyl groups, and thus precipitate proteins, in addition to interfering with essential metabolic activities of microbial cells.
A 0.1% aqueous silver solution is bactericidal and somewhat irritating, whereas a 0.01% solution is bacteriostatic. A 0.5% solution is sometimes applied as a dressing on burns to reduce infection and induce rapid eschar formation. Colloidal silver compounds, which release silver ions slowly, are bacteriostatic and have a more sustained effect. They do not irritate the tissues and have little astringent or caustic effect. They are generally used as mild antiseptics and in ophthalmic preparations.