Metachromasia as the Key to Aminoglycoside Ototoxicity

Abstract

In in-vitro experiments, it was shown that aminoglycosides, in contrast to other antibiotics, inhibited the metachromatic reaction using o-toluidine blue as a basic dye and heparin-Na as a polysulfate-polysaccharide substrate. The inhibitory concentrations were inversely proportional to the free amino groups of aminoglycosides tested. Taking into consideraton (a) that the aminoglycosides antagonize the presence of Ca⁺⁺ and (b) that mechanisms of ototoxicity involve ionic alterations in endolymph, we suggest that: aminoglycoside ototoxicity could be the result of the reaction between aminoglycosides and anionic polyelec-trolytes, of the group of polysulfated polysaccharides, in a metachromatic process.