III. Comparative Quantitative Analysis

Abstract

Hypotheses to explain the selective ototoxicity of aminoglycoside antibiotics may be grouped into two categories: 1) a partition effect and 2) innate hair cell selectivity. The results of this study give evidence that, in fact, both mechanisms may interplay. This conclusion is induced from the observations that following the transtympanic administration of streptomycin, dihydrostreptomycin and neomycin: 1) All three drugs elicited nearly the same topographic pattern and degree of damage in the vestibular compartment. 2) All three drugs elicited nearly the same topographic pattern but widely different degrees of damage in the cochlear compartment (neomycin > > streptomycin > dihydrostreptomycin). 3) Neomycin caused the same devastating cochlear hair cell damage as reported for its systemic administration. 4) Dihydrostreptomycin was significantly more vestibulotoxic than cochleotoxic, and streptomycin was both significantly more cochleotoxic than vestibulotoxic and significantly more cochleotoxic than was dihydrostreptomycin. The latter observations are discussed with regard to contrasts with the literature reporting the drug effects following systemic administration.