The prophylactic effect of thyroxin on kanamycin ototoxicity in guinea pigs.

Guinea pigs receiving intramuscular kanamycin sulfate 400 mg/kg daily and thyroxin 10 mg/kg orally every other day for 9 days were studied to determine whether thyroxin prevents toxic damage to the cochlea from kanamycin. The auditory brainstem response thresholds of wave IV evoked by tone pip stimuli at 4 and 8 kHz were found to be 19.1 dB and 27.2 dB poorer, respectively, for the kanamycin-only animals. Less than 10% of outer hair cells were damaged in 80% of basal turns but without any involvement in the rest turns in animals given thyroxin. Over 50% of outer hair cells were damaged in 65.4% of basal turns and over 50% of the second and third turns were also involved in the kanamycin-only group. Our study suggests that thyroxin reduces the accumulation of kanamycin in the perilymph and prevents the ototoxicity of kanamycin.