Magnitude and pattern of inner and outer hair cell loss in chinchilla as a function of carboplatin dose.

We examined the relationship between carboplatin dose and pattern of IHC and OHC loss in five groups of chinchillas treated with carboplatin: (I) single dose, 38 mg/kg, (II) double dose, 38 mg/kg, (III) double dose, 63 mg/kg, (IV) double dose, 75 mg/kg, and (V) double dose, 100 mg/kg. The pattern of IHC loss was relatively uniform along the length of the cochlea with all doses. Average IHC loss increased from approximately 20 per cent in group I to approximately 100 per cent in groups III, IV and V. Average OHC loss was small or negligible in groups I, II, III and IV; only group V consistently showed large (> 40 per cent) OHC losses. OHC loss progressed along a base-to-apex gradient. The dose of carboplatin which reliably destroyed OHCs was four to five times greater than that needed to damage IHCs.