Development of cochlear sensitivity to aminoglycoside antibiotics.

This study examined the temporal relationship between aminoglycoside ototoxicity and the onset of auditory function in the rat. A single dose of gentamicin sulfate (200 mg/kg) and furosemide (100 mg/kg) was administered on postnatal day 6 (P6), P7, P8, P9, or P10, just before the onset of auditory function. Ototoxicity was assessed by the elevation of auditory brain stem response (ABR) thresholds, recorded once the rats had matured. The ABRs were evoked by acoustic clicks and tone pips. The thresholds of control and P6- and P7-treated animals did not differ significantly from each other. Thresholds of some P8- and all P9-treated animals were elevated. The P10-treated animals were deafened, according to these ABR criteria. These data suggest that the potential for aminoglycoside ototoxicity develops rapidly between P8 and P10, just before the onset of auditory function.