Experimental Ototoxicity of Gentamicin in Squirrel Monkeys

Ototoxicity of gentamicin was investigated in 12 subhuman primate subjects given gentamicin according to different regimens of dosage. Tests for ability to maintain body equilibrium (squirrel monkey rail test), and tests for optokinetic and postrotatory nystagmus were performed in order to assess the vestibular system. Labyrinthine end organs were also studied with electron and light microscopy. In general, disequilibrium occurred within a shorter period of time when high daily doses of gentamicin were given. The total doses seemed to be slightly greater in these subjects before initial ataxic signs were exhibited. The results obtained by the tests of body equilibrium and the electron microscopic findings correlated well, in that the decline in rail threshold was associated with damage to vestibular hair cells. Studies of optokinetic nystagmus indicated that the optokinetic neural pathway was not affected by gentamicin in the doses administered. Pathological changes in the kidneys were mostly tubular degeneration, but glomerular changes were found in some cases.