The ototoxic effects of different doses of gentamicin on the cochlea of pigmented guinea pigs.

The aims of this study were twofold: to obtain baseline data on gentamicin ototoxicity in the pigmented guinea pig, and to compare this data with an earlier study in the albino guinea pig. Animals were given ten consecutive daily doses, subcutaneously, of gentamicin at either 50, 75 or 100 mg/kg. Control animals received equivalent volumes of saline. After 3 weeks the animals were killed and their cochleae examined by light microscopy for hair cell damage. Hair cell damage was mapped onto cochleograms and subsequently quantified. Three sets of comparisons of hair cell damage were made: gentamicin group versus control group for each dose; comparisons between doses; pigmented animals versus albino animals. It was found that cochlear hair cell damage increased with increasing dose of gentamicin: 50 mg/kg was minimally ototoxic, 75 mg/kg was more ototoxic and 100 mg/kg was highly ototoxic, affecting a large extent of the spiral organ. There was a large (statistically significant) difference between the lower doses and the damage caused by 100 mg/kg. The pigmented-albino animal comparison showed albino guinea pigs to be more susceptible to gentamicin.